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 $165.86   4.292%   $172.9787   $172.98   $173.00   $173.00  
  Purchase #2 $213.35   9.260%   $233.1062   $233.11   $233.10   $233.10  
  Purchase #3 $129.40   4.502%   $135.2256   $135.23   $135.25   $135.20  
  Purchase #4 $200.53   10.451%   $221.4874   $221.49   $221.50   $221.50  
  Purchase #5 $230.38   4.861%   $241.5788   $241.58   $241.60   $241.60  
  Purchase #6 $244.65   4.622%   $255.9577   $255.96   $255.95   $256.00  
  Purchase #7 $215.79   3.458%   $223.252   $223.25   $223.25   $223.30  
  7 purchase totals = $1,399.96       $1,483.5864   $1,483.60   $1,483.65   $1,483.70