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 $185.70   13.614%   $210.9812   $210.98   $211.00   $211.00  
  Purchase #2 $7.27   7.848%   $7.8405   $7.84   $7.85   $7.80  
  Purchase #3 $207.36   4.790%   $217.2925   $217.29   $217.30   $217.30  
  Purchase #4 $76.54   8.564%   $83.0949   $83.09   $83.10   $83.10  
  Purchase #5 $108.70   13.482%   $123.3549   $123.35   $123.35   $123.40  
  Purchase #6 $49.39   4.823%   $51.7721   $51.77   $51.75   $51.80  
  Purchase #7 $179.84   11.575%   $200.6565   $200.66   $200.65   $200.70  
  7 purchase totals = $814.80       $894.9926   $894.98   $895.00   $895.10