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 $185.29   4.439%   $193.515   $193.52   $193.50   $193.50  
  Purchase #2 $88.32   10.299%   $97.4161   $97.42   $97.40   $97.40  
  Purchase #3 $61.78   12.434%   $69.4617   $69.46   $69.45   $69.50  
  Purchase #4 $202.65   4.446%   $211.6598   $211.66   $211.65   $211.70  
  Purchase #5 $150.53   5.662%   $159.053   $159.05   $159.05   $159.10  
  Purchase #6 $99.97   4.857%   $104.8255   $104.83   $104.85   $104.80  
  Purchase #7 $168.30   13.390%   $190.8354   $190.84   $190.85   $190.80  
  7 purchase totals = $956.84       $1,026.7665   $1,026.78   $1,026.75   $1,026.80