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 $104.48   13.464%   $118.5472   $118.55   $118.55   $118.50  
  Purchase #2 $221.67   10.739%   $245.4751   $245.48   $245.50   $245.50  
  Purchase #3 $52.77   12.331%   $59.2771   $59.28   $59.30   $59.30  
  Purchase #4 $197.63   4.772%   $207.0609   $207.06   $207.05   $207.10  
  Purchase #5 $249.42   6.651%   $266.0089   $266.01   $266.00   $266.00  
  Purchase #6 $246.57   4.112%   $256.709   $256.71   $256.70   $256.70  
  Purchase #7 $160.43   8.195%   $173.5772   $173.58   $173.60   $173.60  
  7 purchase totals = $1,232.97       $1,326.6554   $1,326.67   $1,326.70   $1,326.70