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 $158.41   4.764%   $165.9567   $165.96   $165.95   $166.00  
  Purchase #2 $238.68   13.234%   $270.2669   $270.27   $270.25   $270.30  
  Purchase #3 $242.58   6.569%   $258.5151   $258.52   $258.50   $258.50  
  Purchase #4 $87.60   5.113%   $92.079   $92.08   $92.10   $92.10  
  Purchase #5 $161.93   3.367%   $167.3822   $167.38   $167.40   $167.40  
  Purchase #6 $245.40   11.184%   $272.8455   $272.85   $272.85   $272.80  
  Purchase #7 $220.32   8.141%   $238.2563   $238.26   $238.25   $238.30  
  7 purchase totals = $1,354.92       $1,465.3017   $1,465.32   $1,465.30   $1,465.40