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 $93.53   11.692%   $104.4655   $104.47   $104.45   $104.50  
  Purchase #2 $206.74   3.319%   $213.6017   $213.60   $213.60   $213.60  
  Purchase #3 $28.78   13.750%   $32.7373   $32.74   $32.75   $32.70  
  Purchase #4 $20.52   12.477%   $23.0803   $23.08   $23.10   $23.10  
  Purchase #5 $211.93   8.318%   $229.5583   $229.56   $229.55   $229.60  
  Purchase #6 $154.93   10.429%   $171.0876   $171.09   $171.10   $171.10  
  Purchase #7 $148.79   12.564%   $167.484   $167.48   $167.50   $167.50  
  7 purchase totals = $865.22       $942.0147   $942.02   $942.05   $942.10