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 $65.37   12.372%   $73.4576   $73.46   $73.45   $73.50  
  Purchase #2 $159.88   9.172%   $174.5442   $174.54   $174.55   $174.50  
  Purchase #3 $171.84   12.585%   $193.4661   $193.47   $193.45   $193.50  
  Purchase #4 $150.86   5.203%   $158.7092   $158.71   $158.70   $158.70  
  Purchase #5 $53.57   9.451%   $58.6329   $58.63   $58.65   $58.60  
  Purchase #6 $217.58   9.196%   $237.5887   $237.59   $237.60   $237.60  
  Purchase #7 $218.33   8.303%   $236.4579   $236.46   $236.45   $236.50  
  7 purchase totals = $1,037.43       $1,132.8566   $1,132.86   $1,132.85   $1,132.90