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 $197.78   3.257%   $204.2217   $204.22   $204.20   $204.20  
  Purchase #2 $99.41   4.272%   $103.6568   $103.66   $103.65   $103.70  
  Purchase #3 $195.98   13.779%   $222.9841   $222.98   $223.00   $223.00  
  Purchase #4 $249.75   7.858%   $269.3754   $269.38   $269.40   $269.40  
  Purchase #5 $170.99   12.657%   $192.6322   $192.63   $192.65   $192.60  
  Purchase #6 $149.85   3.546%   $155.1637   $155.16   $155.15   $155.20  
  Purchase #7 $117.76   7.258%   $126.307   $126.31   $126.30   $126.30  
  7 purchase totals = $1,181.52       $1,274.3409   $1,274.34   $1,274.35   $1,274.40