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 $208.39   8.269%   $225.6218   $225.62   $225.60   $225.60  
  Purchase #2 $227.77   11.662%   $254.3325   $254.33   $254.35   $254.30  
  Purchase #3 $72.53   9.836%   $79.6641   $79.66   $79.65   $79.70  
  Purchase #4 $197.98   7.412%   $212.6543   $212.65   $212.65   $212.70  
  Purchase #5 $160.58   7.119%   $172.0117   $172.01   $172.00   $172.00  
  Purchase #6 $94.44   6.816%   $100.877   $100.88   $100.90   $100.90  
  Purchase #7 $208.63   3.873%   $216.7102   $216.71   $216.70   $216.70  
  7 purchase totals = $1,170.32       $1,261.8716   $1,261.86   $1,261.85   $1,261.90