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 $29.61   13.213%   $33.5224   $33.52   $33.50   $33.50  
  Purchase #2 $154.27   11.383%   $171.8306   $171.83   $171.85   $171.80  
  Purchase #3 $83.89   11.703%   $93.7076   $93.71   $93.70   $93.70  
  Purchase #4 $106.96   7.613%   $115.1029   $115.10   $115.10   $115.10  
  Purchase #5 $112.64   5.663%   $119.0188   $119.02   $119.00   $119.00  
  Purchase #6 $123.97   13.834%   $141.12   $141.12   $141.10   $141.10  
  Purchase #7 $154.62   13.816%   $175.9823   $175.98   $176.00   $176.00  
  7 purchase totals = $765.96       $850.2846   $850.28   $850.25   $850.20