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 $93.67   3.361%   $96.8182   $96.82   $96.80   $96.80  
  Purchase #2 $169.55   11.183%   $188.5108   $188.51   $188.50   $188.50  
  Purchase #3 $210.71   5.262%   $221.7976   $221.80   $221.80   $221.80  
  Purchase #4 $236.35   3.673%   $245.0311   $245.03   $245.05   $245.00  
  Purchase #5 $122.38   9.866%   $134.454   $134.45   $134.45   $134.50  
  Purchase #6 $189.59   5.428%   $199.8809   $199.88   $199.90   $199.90  
  Purchase #7 $121.50   9.293%   $132.791   $132.79   $132.80   $132.80  
  7 purchase totals = $1,143.75       $1,219.2836   $1,219.28   $1,219.30   $1,219.30