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 $202.68   4.691%   $212.1877   $212.19   $212.20   $212.20  
  Purchase #2 $80.99   3.777%   $84.049   $84.05   $84.05   $84.00  
  Purchase #3 $172.48   6.734%   $184.0948   $184.09   $184.10   $184.10  
  Purchase #4 $46.33   8.593%   $50.3111   $50.31   $50.30   $50.30  
  Purchase #5 $178.73   4.297%   $186.41   $186.41   $186.40   $186.40  
  Purchase #6 $137.55   11.691%   $153.631   $153.63   $153.65   $153.60  
  Purchase #7 $134.31   5.441%   $141.6178   $141.62   $141.60   $141.60  
  7 purchase totals = $953.07       $1,012.3014   $1,012.30   $1,012.30   $1,012.20