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 $65.25   12.794%   $73.5981   $73.60   $73.60   $73.60  
  Purchase #2 $68.52   3.701%   $71.0559   $71.06   $71.05   $71.10  
  Purchase #3 $15.31   5.683%   $16.1801   $16.18   $16.20   $16.20  
  Purchase #4 $48.60   6.489%   $51.7537   $51.75   $51.75   $51.80  
  Purchase #5 $162.34   7.717%   $174.8678   $174.87   $174.85   $174.90  
  Purchase #6 $84.42   3.720%   $87.5604   $87.56   $87.55   $87.60  
  Purchase #7 $108.27   10.241%   $119.3579   $119.36   $119.35   $119.40  
  7 purchase totals = $552.71       $594.3739   $594.38   $594.35   $594.60