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 $111.61   6.163%   $118.4885   $118.49   $118.50   $118.50  
  Purchase #2 $24.89   4.336%   $25.9692   $25.97   $25.95   $26.00  
  Purchase #3 $86.37   7.214%   $92.6007   $92.60   $92.60   $92.60  
  Purchase #4 $57.67   9.722%   $63.2767   $63.28   $63.30   $63.30  
  Purchase #5 $74.54   11.148%   $82.8497   $82.85   $82.85   $82.80  
  Purchase #6 $58.29   9.292%   $63.7063   $63.71   $63.70   $63.70  
  Purchase #7 $219.81   3.738%   $228.0265   $228.03   $228.05   $228.00  
  7 purchase totals = $633.18       $674.9176   $674.93   $674.95   $674.90