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 $55.56   12.200%   $62.3383   $62.34   $62.35   $62.30  
  Purchase #2 $22.75   10.103%   $25.0484   $25.05   $25.05   $25.00  
  Purchase #3 $107.54   9.498%   $117.7541   $117.75   $117.75   $117.80  
  Purchase #4 $238.67   6.620%   $254.47   $254.47   $254.45   $254.50  
  Purchase #5 $189.70   8.749%   $206.2969   $206.30   $206.30   $206.30  
  Purchase #6 $234.82   8.157%   $253.9743   $253.97   $253.95   $254.00  
  Purchase #7 $87.84   6.819%   $93.8298   $93.83   $93.85   $93.80  
  7 purchase totals = $936.88       $1,013.7118   $1,013.71   $1,013.70   $1,013.70