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 $173.58   5.624%   $183.3421   $183.34   $183.35   $183.30  
  Purchase #2 $196.90   12.297%   $221.1128   $221.11   $221.10   $221.10  
  Purchase #3 $43.75   5.151%   $46.0036   $46.00   $46.00   $46.00  
  Purchase #4 $61.95   11.229%   $68.9064   $68.91   $68.90   $68.90  
  Purchase #5 $126.33   3.637%   $130.9246   $130.92   $130.90   $130.90  
  Purchase #6 $9.46   11.341%   $10.5329   $10.53   $10.55   $10.50  
  Purchase #7 $241.91   13.228%   $273.9099   $273.91   $273.90   $273.90  
  7 purchase totals = $853.88       $934.7323   $934.72   $934.70   $934.60