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 $68.49   6.797%   $73.1453   $73.15   $73.15   $73.10  
  Purchase #2 $158.52   6.346%   $168.5797   $168.58   $168.60   $168.60  
  Purchase #3 $47.32   10.781%   $52.4216   $52.42   $52.40   $52.40  
  Purchase #4 $220.66   6.452%   $234.897   $234.90   $234.90   $234.90  
  Purchase #5 $191.35   3.201%   $197.4751   $197.48   $197.50   $197.50  
  Purchase #6 $111.48   6.147%   $118.3327   $118.33   $118.35   $118.30  
  Purchase #7 $79.85   9.508%   $87.4421   $87.44   $87.45   $87.40  
  7 purchase totals = $877.67       $932.2935   $932.30   $932.35   $932.20