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 $60.32   5.674%   $63.7426   $63.74   $63.75   $63.70  
  Purchase #2 $135.87   7.424%   $145.957   $145.96   $145.95   $146.00  
  Purchase #3 $37.30   3.594%   $38.6406   $38.64   $38.65   $38.60  
  Purchase #4 $180.84   4.864%   $189.6361   $189.64   $189.65   $189.60  
  Purchase #5 $180.95   8.346%   $196.0521   $196.05   $196.05   $196.10  
  Purchase #6 $28.35   4.495%   $29.6243   $29.62   $29.60   $29.60  
  Purchase #7 $95.61   4.140%   $99.5683   $99.57   $99.55   $99.60  
  7 purchase totals = $719.24       $763.2210   $763.22   $763.20   $763.20