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 $48.90   7.827%   $52.7274   $52.73   $52.75   $52.70  
  Purchase #2 $189.86   5.859%   $200.9839   $200.98   $201.00   $201.00  
  Purchase #3 $32.90   3.548%   $34.0673   $34.07   $34.05   $34.10  
  Purchase #4 $124.41   5.416%   $131.148   $131.15   $131.15   $131.10  
  Purchase #5 $121.72   3.803%   $126.349   $126.35   $126.35   $126.30  
  Purchase #6 $154.69   7.381%   $166.1077   $166.11   $166.10   $166.10  
  Purchase #7 $67.35   12.415%   $75.7115   $75.71   $75.70   $75.70  
  7 purchase totals = $739.83       $787.0948   $787.10   $787.10   $787.00