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 $21.97   7.872%   $23.6995   $23.70   $23.70   $23.70  
  Purchase #2 $44.56   3.797%   $46.2519   $46.25   $46.25   $46.30  
  Purchase #3 $198.70   9.818%   $218.2084   $218.21   $218.20   $218.20  
  Purchase #4 $104.29   7.470%   $112.0805   $112.08   $112.10   $112.10  
  Purchase #5 $116.85   3.806%   $121.2973   $121.30   $121.30   $121.30  
  Purchase #6 $88.31   3.706%   $91.5828   $91.58   $91.60   $91.60  
  Purchase #7 $23.86   4.206%   $24.8636   $24.86   $24.85   $24.90  
  7 purchase totals = $598.54       $637.9840   $637.98   $638.00   $638.10