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 $233.49   8.571%   $253.5024   $253.50   $253.50   $253.50  
  Purchase #2 $219.25   12.543%   $246.7505   $246.75   $246.75   $246.80  
  Purchase #3 $92.37   6.625%   $98.4895   $98.49   $98.50   $98.50  
  Purchase #4 $222.74   3.135%   $229.7229   $229.72   $229.70   $229.70  
  Purchase #5 $225.75   11.438%   $251.5713   $251.57   $251.55   $251.60  
  Purchase #6 $122.86   8.640%   $133.4751   $133.48   $133.50   $133.50  
  Purchase #7 $123.51   7.421%   $132.6757   $132.68   $132.70   $132.70  
  7 purchase totals = $1,239.97       $1,346.1874   $1,346.19   $1,346.20   $1,346.30