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 $60.35   4.617%   $63.1364   $63.14   $63.15   $63.10  
  Purchase #2 $238.85   5.400%   $251.7479   $251.75   $251.75   $251.70  
  Purchase #3 $125.58   6.169%   $133.327   $133.33   $133.35   $133.30  
  Purchase #4 $128.45   9.685%   $140.8904   $140.89   $140.90   $140.90  
  Purchase #5 $219.41   9.525%   $240.3088   $240.31   $240.30   $240.30  
  Purchase #6 $31.90   7.206%   $34.1987   $34.20   $34.20   $34.20  
  Purchase #7 $121.47   13.281%   $137.6024   $137.60   $137.60   $137.60  
  7 purchase totals = $926.01       $1,001.2116   $1,001.22   $1,001.25   $1,001.10