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 $195.69   12.866%   $220.8675   $220.87   $220.85   $220.90  
  Purchase #2 $22.56   11.297%   $25.1086   $25.11   $25.10   $25.10  
  Purchase #3 $187.27   3.616%   $194.0417   $194.04   $194.05   $194.00  
  Purchase #4 $155.69   7.111%   $166.7611   $166.76   $166.75   $166.80  
  Purchase #5 $88.50   7.615%   $95.2393   $95.24   $95.25   $95.20  
  Purchase #6 $104.60   7.562%   $112.5099   $112.51   $112.50   $112.50  
  Purchase #7 $240.84   5.362%   $253.7538   $253.75   $253.75   $253.80  
  7 purchase totals = $995.15       $1,068.2819   $1,068.28   $1,068.25   $1,068.30