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 $208.84   6.817%   $223.0766   $223.08   $223.10   $223.10  
  Purchase #2 $130.59   3.597%   $135.2873   $135.29   $135.30   $135.30  
  Purchase #3 $195.82   8.753%   $212.9601   $212.96   $212.95   $213.00  
  Purchase #4 $248.96   9.358%   $272.2577   $272.26   $272.25   $272.30  
  Purchase #5 $140.98   3.518%   $145.9397   $145.94   $145.95   $145.90  
  Purchase #6 $36.45   12.133%   $40.8725   $40.87   $40.85   $40.90  
  Purchase #7 $204.80   8.385%   $221.9725   $221.97   $221.95   $222.00  
  7 purchase totals = $1,166.44       $1,252.3664   $1,252.37   $1,252.35   $1,252.50