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 $211.41   8.629%   $229.6526   $229.65   $229.65   $229.70  
  Purchase #2 $245.35   13.791%   $279.1862   $279.19   $279.20   $279.20  
  Purchase #3 $172.53   3.598%   $178.7376   $178.74   $178.75   $178.70  
  Purchase #4 $184.67   6.756%   $197.1463   $197.15   $197.15   $197.10  
  Purchase #5 $23.56   12.765%   $26.5674   $26.57   $26.55   $26.60  
  Purchase #6 $208.36   13.540%   $236.5719   $236.57   $236.55   $236.60  
  Purchase #7 $193.85   7.821%   $209.011   $209.01   $209.00   $209.00  
  7 purchase totals = $1,239.73       $1,356.8730   $1,356.88   $1,356.85   $1,356.90