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 $178.63   12.701%   $201.3178   $201.32   $201.30   $201.30  
  Purchase #2 $221.65   7.523%   $238.3247   $238.32   $238.30   $238.30  
  Purchase #3 $57.32   10.859%   $63.5444   $63.54   $63.55   $63.50  
  Purchase #4 $74.69   10.317%   $82.3958   $82.40   $82.40   $82.40  
  Purchase #5 $210.41   5.594%   $222.1803   $222.18   $222.20   $222.20  
  Purchase #6 $244.96   9.813%   $268.9979   $269.00   $269.00   $269.00  
  Purchase #7 $183.43   5.770%   $194.0139   $194.01   $194.00   $194.00  
  7 purchase totals = $1,171.09       $1,270.7748   $1,270.77   $1,270.75   $1,270.70