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 $156.62   3.463%   $162.0438   $162.04   $162.05   $162.00  
  Purchase #2 $226.66   5.132%   $238.2922   $238.29   $238.30   $238.30  
  Purchase #3 $22.36   9.565%   $24.4987   $24.50   $24.50   $24.50  
  Purchase #4 $161.79   3.430%   $167.3394   $167.34   $167.35   $167.30  
  Purchase #5 $243.65   5.378%   $256.7535   $256.75   $256.75   $256.80  
  Purchase #6 $49.46   4.478%   $51.6748   $51.67   $51.65   $51.70  
  Purchase #7 $20.78   12.508%   $23.3792   $23.38   $23.40   $23.40  
  7 purchase totals = $881.32       $923.9816   $923.97   $924.00   $924.00