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 $92.98   12.627%   $104.7206   $104.72   $104.70   $104.70  
  Purchase #2 $8.25   6.493%   $8.7857   $8.79   $8.80   $8.80  
  Purchase #3 $50.87   3.535%   $52.6683   $52.67   $52.65   $52.70  
  Purchase #4 $217.60   8.800%   $236.7488   $236.75   $236.75   $236.70  
  Purchase #5 $113.52   13.204%   $128.5092   $128.51   $128.50   $128.50  
  Purchase #6 $53.98   11.117%   $59.981   $59.98   $60.00   $60.00  
  Purchase #7 $241.75   8.150%   $261.4526   $261.45   $261.45   $261.50  
  7 purchase totals = $778.95       $852.8662   $852.87   $852.85   $852.90