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 $58.33   6.638%   $62.2019   $62.20   $62.20   $62.20  
  Purchase #2 $84.79   7.448%   $91.1052   $91.11   $91.10   $91.10  
  Purchase #3 $90.82   11.635%   $101.3869   $101.39   $101.40   $101.40  
  Purchase #4 $232.27   9.194%   $253.6249   $253.62   $253.60   $253.60  
  Purchase #5 $18.29   12.261%   $20.5325   $20.53   $20.55   $20.50  
  Purchase #6 $172.65   4.812%   $180.9579   $180.96   $180.95   $181.00  
  Purchase #7 $96.50   12.142%   $108.217   $108.22   $108.20   $108.20  
  7 purchase totals = $753.65       $818.0263   $818.03   $818.00   $818.00