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 $167.42   11.216%   $186.1978   $186.20   $186.20   $186.20  
  Purchase #2 $242.74   13.674%   $275.9323   $275.93   $275.95   $275.90  
  Purchase #3 $73.30   6.111%   $77.7794   $77.78   $77.80   $77.80  
  Purchase #4 $83.44   12.212%   $93.6297   $93.63   $93.65   $93.60  
  Purchase #5 $217.41   10.176%   $239.5336   $239.53   $239.55   $239.50  
  Purchase #6 $150.96   7.359%   $162.0691   $162.07   $162.05   $162.10  
  Purchase #7 $87.41   4.280%   $91.1511   $91.15   $91.15   $91.20  
  7 purchase totals = $1,022.68       $1,126.2930   $1,126.29   $1,126.35   $1,126.30