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 $198.73   6.471%   $211.5898   $211.59   $211.60   $211.60  
  Purchase #2 $124.87   11.159%   $138.8042   $138.80   $138.80   $138.80  
  Purchase #3 $53.81   6.736%   $57.4346   $57.43   $57.45   $57.40  
  Purchase #4 $91.74   11.379%   $102.1791   $102.18   $102.20   $102.20  
  Purchase #5 $119.35   5.644%   $126.0861   $126.09   $126.10   $126.10  
  Purchase #6 $143.36   13.442%   $162.6305   $162.63   $162.65   $162.60  
  Purchase #7 $209.62   13.557%   $238.0382   $238.04   $238.05   $238.00  
  7 purchase totals = $941.48       $1,036.7625   $1,036.76   $1,036.85   $1,036.70