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 $44.56   7.623%   $47.9568   $47.96   $47.95   $48.00  
  Purchase #2 $143.53   11.485%   $160.0144   $160.01   $160.00   $160.00  
  Purchase #3 $111.70   6.743%   $119.2319   $119.23   $119.25   $119.20  
  Purchase #4 $229.94   4.795%   $240.9656   $240.97   $240.95   $241.00  
  Purchase #5 $110.85   4.199%   $115.5046   $115.50   $115.50   $115.50  
  Purchase #6 $131.59   5.242%   $138.4879   $138.49   $138.50   $138.50  
  Purchase #7 $163.56   10.859%   $181.321   $181.32   $181.30   $181.30  
  7 purchase totals = $935.73       $1,003.4822   $1,003.48   $1,003.45   $1,003.50