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 $69.95   5.427%   $73.7462   $73.75   $73.75   $73.70  
  Purchase #2 $186.72   3.192%   $192.6801   $192.68   $192.70   $192.70  
  Purchase #3 $21.45   13.554%   $24.3573   $24.36   $24.35   $24.40  
  Purchase #4 $197.48   12.822%   $222.8009   $222.80   $222.80   $222.80  
  Purchase #5 $130.46   11.776%   $145.823   $145.82   $145.80   $145.80  
  Purchase #6 $233.69   10.384%   $257.9564   $257.96   $257.95   $258.00  
  Purchase #7 $11.74   13.616%   $13.3385   $13.34   $13.35   $13.30  
  7 purchase totals = $851.49       $930.7024   $930.71   $930.70   $930.70