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 $47.93   10.634%   $53.0269   $53.03   $53.05   $53.00  
  Purchase #2 $171.84   8.677%   $186.7506   $186.75   $186.75   $186.80  
  Purchase #3 $17.77   7.743%   $19.1459   $19.15   $19.15   $19.10  
  Purchase #4 $16.27   13.737%   $18.505   $18.51   $18.50   $18.50  
  Purchase #5 $171.65   5.170%   $180.5243   $180.52   $180.50   $180.50  
  Purchase #6 $216.25   12.815%   $243.9624   $243.96   $243.95   $244.00  
  Purchase #7 $28.71   8.121%   $31.0415   $31.04   $31.05   $31.00  
  7 purchase totals = $670.42       $732.9566   $732.96   $732.95   $732.90