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 $91.96   3.665%   $95.3303   $95.33   $95.35   $95.30  
  Purchase #2 $14.73   3.832%   $15.2945   $15.29   $15.30   $15.30  
  Purchase #3 $143.80   12.401%   $161.6326   $161.63   $161.65   $161.60  
  Purchase #4 $51.92   13.666%   $59.0154   $59.02   $59.00   $59.00  
  Purchase #5 $66.60   11.609%   $74.3316   $74.33   $74.35   $74.30  
  Purchase #6 $35.43   3.116%   $36.534   $36.53   $36.55   $36.50  
  Purchase #7 $138.76   7.797%   $149.5791   $149.58   $149.60   $149.60  
  7 purchase totals = $543.20       $591.7175   $591.71   $591.80   $591.60