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 $243.49   4.198%   $253.7117   $253.71   $253.70   $253.70  
  Purchase #2 $239.97   11.513%   $267.5977   $267.60   $267.60   $267.60  
  Purchase #3 $62.51   8.657%   $67.9215   $67.92   $67.90   $67.90  
  Purchase #4 $126.47   5.760%   $133.7547   $133.75   $133.75   $133.80  
  Purchase #5 $145.27   9.522%   $159.1026   $159.10   $159.10   $159.10  
  Purchase #6 $138.93   4.295%   $144.897   $144.90   $144.90   $144.90  
  Purchase #7 $219.91   7.442%   $236.2757   $236.28   $236.30   $236.30  
  7 purchase totals = $1,176.55       $1,263.2609   $1,263.26   $1,263.25   $1,263.30