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 $80.29   3.406%   $83.0247   $83.02   $83.00   $83.00  
  Purchase #2 $126.49   4.520%   $132.2073   $132.21   $132.20   $132.20  
  Purchase #3 $40.36   11.779%   $45.114   $45.11   $45.10   $45.10  
  Purchase #4 $36.97   7.517%   $39.749   $39.75   $39.75   $39.70  
  Purchase #5 $184.69   10.570%   $204.2117   $204.21   $204.20   $204.20  
  Purchase #6 $212.99   11.235%   $236.9194   $236.92   $236.90   $236.90  
  Purchase #7 $243.81   12.136%   $273.3988   $273.40   $273.40   $273.40  
  7 purchase totals = $925.60       $1,014.6249   $1,014.62   $1,014.55   $1,014.50