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 $52.58   5.801%   $55.6302   $55.63   $55.65   $55.60  
  Purchase #2 $127.42   4.397%   $133.0227   $133.02   $133.00   $133.00  
  Purchase #3 $204.94   9.132%   $223.6551   $223.66   $223.65   $223.70  
  Purchase #4 $250.35   10.424%   $276.4465   $276.45   $276.45   $276.40  
  Purchase #5 $31.71   5.717%   $33.5229   $33.52   $33.50   $33.50  
  Purchase #6 $169.32   11.618%   $188.9916   $188.99   $189.00   $189.00  
  Purchase #7 $105.54   4.568%   $110.3611   $110.36   $110.35   $110.40  
  7 purchase totals = $941.86       $1,021.6301   $1,021.63   $1,021.60   $1,021.60