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 $212.38   3.442%   $219.6901   $219.69   $219.70   $219.70  
  Purchase #2 $244.59   3.827%   $253.9505   $253.95   $253.95   $254.00  
  Purchase #3 $182.73   12.681%   $205.902   $205.90   $205.90   $205.90  
  Purchase #4 $167.44   9.114%   $182.7005   $182.70   $182.70   $182.70  
  Purchase #5 $29.59   4.430%   $30.9008   $30.90   $30.90   $30.90  
  Purchase #6 $237.59   12.403%   $267.0583   $267.06   $267.05   $267.10  
  Purchase #7 $81.91   7.444%   $88.0074   $88.01   $88.00   $88.00  
  7 purchase totals = $1,156.23       $1,248.2096   $1,248.21   $1,248.20   $1,248.30