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 $173.52   11.839%   $194.063   $194.06   $194.05   $194.10  
  Purchase #2 $15.97   9.597%   $17.5026   $17.50   $17.50   $17.50  
  Purchase #3 $58.77   8.633%   $63.8436   $63.84   $63.85   $63.80  
  Purchase #4 $48.98   12.426%   $55.0663   $55.07   $55.05   $55.10  
  Purchase #5 $135.43   9.862%   $148.7861   $148.79   $148.80   $148.80  
  Purchase #6 $63.56   7.744%   $68.4821   $68.48   $68.50   $68.50  
  Purchase #7 $204.62   6.436%   $217.7893   $217.79   $217.80   $217.80  
  7 purchase totals = $700.85       $765.5330   $765.53   $765.55   $765.60