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 $96.86   7.721%   $104.3386   $104.34   $104.35   $104.30  
  Purchase #2 $170.92   3.508%   $176.9159   $176.92   $176.90   $176.90  
  Purchase #3 $120.57   3.824%   $125.1806   $125.18   $125.20   $125.20  
  Purchase #4 $138.90   4.805%   $145.5741   $145.57   $145.55   $145.60  
  Purchase #5 $17.33   13.341%   $19.642   $19.64   $19.65   $19.60  
  Purchase #6 $84.88   11.384%   $94.5427   $94.54   $94.55   $94.50  
  Purchase #7 $246.95   7.329%   $265.049   $265.05   $265.05   $265.00  
  7 purchase totals = $876.41       $931.2429   $931.24   $931.25   $931.10