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 $58.51   13.304%   $66.2942   $66.29   $66.30   $66.30  
  Purchase #2 $235.46   3.278%   $243.1784   $243.18   $243.20   $243.20  
  Purchase #3 $151.34   12.446%   $170.1758   $170.18   $170.20   $170.20  
  Purchase #4 $206.79   3.146%   $213.2956   $213.30   $213.30   $213.30  
  Purchase #5 $42.66   3.666%   $44.2239   $44.22   $44.20   $44.20  
  Purchase #6 $126.29   7.190%   $135.3703   $135.37   $135.35   $135.40  
  Purchase #7 $120.27   13.644%   $136.6796   $136.68   $136.70   $136.70  
  7 purchase totals = $941.32       $1,009.2178   $1,009.22   $1,009.25   $1,009.30