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 $55.61   7.830%   $59.9643   $59.96   $59.95   $60.00  
  Purchase #2 $243.63   13.552%   $276.6467   $276.65   $276.65   $276.60  
  Purchase #3 $227.77   13.426%   $258.3504   $258.35   $258.35   $258.40  
  Purchase #4 $200.46   4.293%   $209.0657   $209.07   $209.05   $209.10  
  Purchase #5 $37.84   4.863%   $39.6802   $39.68   $39.70   $39.70  
  Purchase #6 $162.54   4.325%   $169.5699   $169.57   $169.55   $169.60  
  Purchase #7 $36.46   12.476%   $41.0087   $41.01   $41.00   $41.00  
  7 purchase totals = $964.31       $1,054.2859   $1,054.29   $1,054.25   $1,054.40