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 $48.72   8.716%   $52.9664   $52.97   $52.95   $53.00  
  Purchase #2 $194.86   5.292%   $205.172   $205.17   $205.15   $205.20  
  Purchase #3 $113.65   12.574%   $127.9404   $127.94   $127.95   $127.90  
  Purchase #4 $206.87   3.434%   $213.9739   $213.97   $213.95   $214.00  
  Purchase #5 $220.76   8.605%   $239.7564   $239.76   $239.75   $239.80  
  Purchase #6 $46.84   6.672%   $49.9652   $49.97   $49.95   $50.00  
  Purchase #7 $126.36   6.456%   $134.5178   $134.52   $134.50   $134.50  
  7 purchase totals = $958.06       $1,024.2921   $1,024.30   $1,024.20   $1,024.40