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 $165.35   11.796%   $184.8547   $184.85   $184.85   $184.90  
  Purchase #2 $223.46   8.811%   $243.1491   $243.15   $243.15   $243.10  
  Purchase #3 $67.94   10.649%   $75.1749   $75.17   $75.15   $75.20  
  Purchase #4 $74.68   5.431%   $78.7359   $78.74   $78.75   $78.70  
  Purchase #5 $226.93   3.331%   $234.489   $234.49   $234.50   $234.50  
  Purchase #6 $139.30   12.125%   $156.1901   $156.19   $156.20   $156.20  
  Purchase #7 $48.78   6.611%   $52.0048   $52.00   $52.00   $52.00  
  7 purchase totals = $946.44       $1,024.5985   $1,024.59   $1,024.60   $1,024.60