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 $118.31   8.445%   $128.3013   $128.30   $128.30   $128.30  
  Purchase #2 $167.60   11.794%   $187.3667   $187.37   $187.35   $187.40  
  Purchase #3 $213.62   10.202%   $235.4135   $235.41   $235.40   $235.40  
  Purchase #4 $192.84   12.343%   $216.6422   $216.64   $216.65   $216.60  
  Purchase #5 $93.64   10.664%   $103.6258   $103.63   $103.65   $103.60  
  Purchase #6 $166.62   6.191%   $176.9354   $176.94   $176.95   $176.90  
  Purchase #7 $12.86   9.147%   $14.0363   $14.04   $14.05   $14.00  
  7 purchase totals = $965.49       $1,062.3212   $1,062.33   $1,062.35   $1,062.20