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 $191.33   7.148%   $205.0063   $205.01   $205.00   $205.00  
  Purchase #2 $74.93   10.349%   $82.6845   $82.68   $82.70   $82.70  
  Purchase #3 $201.73   12.421%   $226.7869   $226.79   $226.80   $226.80  
  Purchase #4 $39.41   3.745%   $40.8859   $40.89   $40.90   $40.90  
  Purchase #5 $106.62   12.756%   $120.2204   $120.22   $120.20   $120.20  
  Purchase #6 $201.88   11.706%   $225.5121   $225.51   $225.50   $225.50  
  Purchase #7 $26.91   7.693%   $28.9802   $28.98   $29.00   $29.00  
  7 purchase totals = $842.81       $930.0763   $930.08   $930.10   $930.10