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 $96.92   10.809%   $107.3961   $107.40   $107.40   $107.40  
  Purchase #2 $214.65   10.598%   $237.3986   $237.40   $237.40   $237.40  
  Purchase #3 $52.99   11.296%   $58.9758   $58.98   $59.00   $59.00  
  Purchase #4 $48.62   8.167%   $52.5908   $52.59   $52.60   $52.60  
  Purchase #5 $204.50   8.390%   $221.6576   $221.66   $221.65   $221.70  
  Purchase #6 $71.79   4.798%   $75.2345   $75.23   $75.25   $75.20  
  Purchase #7 $247.79   8.341%   $268.4582   $268.46   $268.45   $268.50  
  7 purchase totals = $937.26       $1,021.7116   $1,021.72   $1,021.75   $1,021.80