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 $246.73   4.462%   $257.7391   $257.74   $257.75   $257.70  
  Purchase #2 $236.50   11.607%   $263.9506   $263.95   $263.95   $264.00  
  Purchase #3 $38.31   8.545%   $41.5836   $41.58   $41.60   $41.60  
  Purchase #4 $124.37   11.364%   $138.5034   $138.50   $138.50   $138.50  
  Purchase #5 $180.73   11.203%   $200.9772   $200.98   $201.00   $201.00  
  Purchase #6 $148.83   6.563%   $158.5977   $158.60   $158.60   $158.60  
  Purchase #7 $38.73   8.359%   $41.9674   $41.97   $41.95   $42.00  
  7 purchase totals = $1,014.20       $1,103.3190   $1,103.32   $1,103.35   $1,103.40