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 $155.32   7.701%   $167.2812   $167.28   $167.30   $167.30  
  Purchase #2 $214.96   9.553%   $235.4951   $235.50   $235.50   $235.50  
  Purchase #3 $125.27   8.690%   $136.156   $136.16   $136.15   $136.20  
  Purchase #4 $104.99   10.815%   $116.3447   $116.34   $116.35   $116.30  
  Purchase #5 $23.57   6.451%   $25.0905   $25.09   $25.10   $25.10  
  Purchase #6 $75.40   9.504%   $82.566   $82.57   $82.55   $82.60  
  Purchase #7 $65.41   10.461%   $72.2525   $72.25   $72.25   $72.30  
  7 purchase totals = $764.92       $835.1860   $835.19   $835.20   $835.30