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 $225.49   3.309%   $232.9515   $232.95   $232.95   $233.00  
  Purchase #2 $136.52   13.802%   $155.3625   $155.36   $155.35   $155.40  
  Purchase #3 $229.40   12.351%   $257.7332   $257.73   $257.75   $257.70  
  Purchase #4 $83.63   9.113%   $91.2512   $91.25   $91.25   $91.30  
  Purchase #5 $119.33   8.759%   $129.7821   $129.78   $129.80   $129.80  
  Purchase #6 $121.94   3.707%   $126.4603   $126.46   $126.45   $126.50  
  Purchase #7 $79.43   10.345%   $87.647   $87.65   $87.65   $87.60  
  7 purchase totals = $995.74       $1,081.1878   $1,081.18   $1,081.20   $1,081.30