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 $202.98   10.874%   $225.052   $225.05   $225.05   $225.10  
  Purchase #2 $219.34   4.123%   $228.3834   $228.38   $228.40   $228.40  
  Purchase #3 $27.98   12.556%   $31.4932   $31.49   $31.50   $31.50  
  Purchase #4 $133.42   6.395%   $141.9522   $141.95   $141.95   $142.00  
  Purchase #5 $84.80   7.797%   $91.4119   $91.41   $91.40   $91.40  
  Purchase #6 $227.92   4.417%   $237.9872   $237.99   $238.00   $238.00  
  Purchase #7 $59.79   10.685%   $66.1786   $66.18   $66.20   $66.20  
  7 purchase totals = $956.23       $1,022.4585   $1,022.45   $1,022.50   $1,022.60