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 $24.97   3.225%   $25.7753   $25.78   $25.80   $25.80  
  Purchase #2 $234.79   9.184%   $256.3531   $256.35   $256.35   $256.40  
  Purchase #3 $103.28   13.618%   $117.3447   $117.34   $117.35   $117.30  
  Purchase #4 $238.29   10.275%   $262.7743   $262.77   $262.75   $262.80  
  Purchase #5 $157.87   6.792%   $168.5925   $168.59   $168.60   $168.60  
  Purchase #6 $160.75   6.427%   $171.0814   $171.08   $171.10   $171.10  
  Purchase #7 $63.33   8.131%   $68.4794   $68.48   $68.50   $68.50  
  7 purchase totals = $983.28       $1,070.4007   $1,070.39   $1,070.45   $1,070.50