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 $197.37   12.779%   $222.5919   $222.59   $222.60   $222.60  
  Purchase #2 $67.96   8.782%   $73.9282   $73.93   $73.95   $73.90  
  Purchase #3 $73.64   13.311%   $83.4422   $83.44   $83.45   $83.40  
  Purchase #4 $232.41   5.568%   $245.3506   $245.35   $245.35   $245.40  
  Purchase #5 $189.72   9.165%   $207.1078   $207.11   $207.10   $207.10  
  Purchase #6 $147.92   3.675%   $153.3561   $153.36   $153.35   $153.40  
  Purchase #7 $46.42   7.628%   $49.9609   $49.96   $49.95   $50.00  
  7 purchase totals = $955.44       $1,035.7377   $1,035.74   $1,035.75   $1,035.80