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 $46.96   6.415%   $49.9725   $49.97   $49.95   $50.00  
  Purchase #2 $215.83   6.735%   $230.3662   $230.37   $230.35   $230.40  
  Purchase #3 $160.53   12.478%   $180.5609   $180.56   $180.55   $180.60  
  Purchase #4 $178.92   3.452%   $185.0963   $185.10   $185.10   $185.10  
  Purchase #5 $146.59   13.741%   $166.7329   $166.73   $166.75   $166.70  
  Purchase #6 $68.99   5.446%   $72.7472   $72.75   $72.75   $72.70  
  Purchase #7 $144.95   11.350%   $161.4018   $161.40   $161.40   $161.40  
  7 purchase totals = $962.77       $1,046.8778   $1,046.88   $1,046.85   $1,046.90