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 $126.41   6.278%   $134.346   $134.35   $134.35   $134.30  
  Purchase #2 $168.27   12.576%   $189.4316   $189.43   $189.45   $189.40  
  Purchase #3 $50.32   7.392%   $54.0397   $54.04   $54.05   $54.00  
  Purchase #4 $33.79   8.635%   $36.7078   $36.71   $36.70   $36.70  
  Purchase #5 $244.64   5.586%   $258.3056   $258.31   $258.30   $258.30  
  Purchase #6 $151.98   11.811%   $169.9304   $169.93   $169.95   $169.90  
  Purchase #7 $211.77   5.233%   $222.8519   $222.85   $222.85   $222.90  
  7 purchase totals = $987.18       $1,065.6130   $1,065.62   $1,065.65   $1,065.50