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 $238.43   11.661%   $266.2333   $266.23   $266.25   $266.20  
  Purchase #2 $176.29   13.793%   $200.6057   $200.61   $200.60   $200.60  
  Purchase #3 $93.43   10.633%   $103.3644   $103.36   $103.35   $103.40  
  Purchase #4 $152.71   9.325%   $166.9502   $166.95   $166.95   $167.00  
  Purchase #5 $160.86   12.506%   $180.9772   $180.98   $181.00   $181.00  
  Purchase #6 $30.73   6.778%   $32.8129   $32.81   $32.80   $32.80  
  Purchase #7 $184.67   12.483%   $207.7224   $207.72   $207.70   $207.70  
  7 purchase totals = $1,037.12       $1,158.6661   $1,158.66   $1,158.65   $1,158.70