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 $211.53   6.276%   $224.8056   $224.81   $224.80   $224.80  
  Purchase #2 $243.64   8.359%   $264.0059   $264.01   $264.00   $264.00  
  Purchase #3 $98.67   8.428%   $106.9859   $106.99   $107.00   $107.00  
  Purchase #4 $234.57   12.571%   $264.0578   $264.06   $264.05   $264.10  
  Purchase #5 $32.30   13.522%   $36.6676   $36.67   $36.65   $36.70  
  Purchase #6 $242.50   10.221%   $267.2859   $267.29   $267.30   $267.30  
  Purchase #7 $233.95   12.398%   $262.9551   $262.96   $262.95   $263.00  
  7 purchase totals = $1,297.16       $1,426.7638   $1,426.79   $1,426.75   $1,426.90