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 $189.82   8.493%   $205.9414   $205.94   $205.95   $205.90  
  Purchase #2 $226.60   5.661%   $239.4278   $239.43   $239.45   $239.40  
  Purchase #3 $84.28   12.104%   $94.4813   $94.48   $94.50   $94.50  
  Purchase #4 $223.30   9.124%   $243.6739   $243.67   $243.65   $243.70  
  Purchase #5 $89.48   3.624%   $92.7228   $92.72   $92.70   $92.70  
  Purchase #6 $170.92   12.628%   $192.5038   $192.50   $192.50   $192.50  
  Purchase #7 $250.35   12.143%   $280.75   $280.75   $280.75   $280.80  
  7 purchase totals = $1,234.75       $1,349.5010   $1,349.49   $1,349.50   $1,349.50