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 $64.46   6.117%   $68.403   $68.40   $68.40   $68.40  
  Purchase #2 $132.53   4.586%   $138.6078   $138.61   $138.60   $138.60  
  Purchase #3 $164.41   3.286%   $169.8125   $169.81   $169.80   $169.80  
  Purchase #4 $189.61   11.439%   $211.2995   $211.30   $211.30   $211.30  
  Purchase #5 $40.55   7.566%   $43.618   $43.62   $43.60   $43.60  
  Purchase #6 $225.75   4.229%   $235.297   $235.30   $235.30   $235.30  
  Purchase #7 $235.99   6.683%   $251.7612   $251.76   $251.75   $251.80  
  7 purchase totals = $1,053.30       $1,118.7990   $1,118.80   $1,118.75   $1,118.80