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 $95.76   11.718%   $106.9812   $106.98   $107.00   $107.00  
  Purchase #2 $172.61   12.566%   $194.3002   $194.30   $194.30   $194.30  
  Purchase #3 $58.62   4.385%   $61.1905   $61.19   $61.20   $61.20  
  Purchase #4 $120.41   3.816%   $125.0048   $125.00   $125.00   $125.00  
  Purchase #5 $15.85   3.382%   $16.386   $16.39   $16.40   $16.40  
  Purchase #6 $88.95   6.454%   $94.6908   $94.69   $94.70   $94.70  
  Purchase #7 $47.58   6.273%   $50.5647   $50.56   $50.55   $50.60  
  7 purchase totals = $599.78       $649.1182   $649.11   $649.15   $649.20