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 $74.36   5.722%   $78.6149   $78.61   $78.60   $78.60  
  Purchase #2 $185.97   9.612%   $203.8454   $203.85   $203.85   $203.80  
  Purchase #3 $132.98   7.514%   $142.9721   $142.97   $142.95   $143.00  
  Purchase #4 $95.51   3.495%   $98.8481   $98.85   $98.85   $98.80  
  Purchase #5 $79.30   10.424%   $87.5662   $87.57   $87.55   $87.60  
  Purchase #6 $98.56   10.297%   $108.7087   $108.71   $108.70   $108.70  
  Purchase #7 $67.90   5.305%   $71.5021   $71.50   $71.50   $71.50  
  7 purchase totals = $734.58       $792.0575   $792.06   $792.00   $792.00