Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $173.82   4.419%   $181.5011   $181.50   $181.50   $181.50  
  Purchase #2 $209.93   11.668%   $234.4246   $234.42   $234.40   $234.40  
  Purchase #3 $201.29   6.448%   $214.2692   $214.27   $214.25   $214.30  
  Purchase #4 $229.98   7.544%   $247.3297   $247.33   $247.35   $247.30  
  Purchase #5 $141.25   3.206%   $145.7785   $145.78   $145.80   $145.80  
  Purchase #6 $194.80   11.623%   $217.4416   $217.44   $217.45   $217.40  
  Purchase #7 $225.66   7.542%   $242.6793   $242.68   $242.70   $242.70  
  7 purchase totals = $1,376.73       $1,483.4240   $1,483.42   $1,483.45   $1,483.40