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 $246.35   6.761%   $263.0057   $263.01   $263.00   $263.00  
  Purchase #2 $168.31   11.495%   $187.6572   $187.66   $187.65   $187.70  
  Purchase #3 $53.56   9.581%   $58.6916   $58.69   $58.70   $58.70  
  Purchase #4 $65.49   13.366%   $74.2434   $74.24   $74.25   $74.20  
  Purchase #5 $32.59   12.496%   $36.6624   $36.66   $36.65   $36.70  
  Purchase #6 $125.43   4.263%   $130.7771   $130.78   $130.80   $130.80  
  Purchase #7 $230.77   13.855%   $262.7432   $262.74   $262.75   $262.70  
  7 purchase totals = $922.50       $1,013.7806   $1,013.78   $1,013.80   $1,013.80