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 $86.69   8.652%   $94.1904   $94.19   $94.20   $94.20  
  Purchase #2 $180.90   10.800%   $200.4372   $200.44   $200.45   $200.40  
  Purchase #3 $235.84   4.553%   $246.5778   $246.58   $246.60   $246.60  
  Purchase #4 $24.96   11.299%   $27.7802   $27.78   $27.80   $27.80  
  Purchase #5 $214.96   9.107%   $234.5364   $234.54   $234.55   $234.50  
  Purchase #6 $219.38   9.227%   $239.6222   $239.62   $239.60   $239.60  
  Purchase #7 $17.28   12.161%   $19.3814   $19.38   $19.40   $19.40  
  7 purchase totals = $980.01       $1,062.5256   $1,062.53   $1,062.60   $1,062.50