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 $70.97   12.152%   $79.5943   $79.59   $79.60   $79.60  
  Purchase #2 $178.66   11.583%   $199.3542   $199.35   $199.35   $199.40  
  Purchase #3 $68.33   7.865%   $73.7042   $73.70   $73.70   $73.70  
  Purchase #4 $206.84   7.315%   $221.9703   $221.97   $221.95   $222.00  
  Purchase #5 $211.71   12.846%   $238.9063   $238.91   $238.90   $238.90  
  Purchase #6 $87.63   6.758%   $93.552   $93.55   $93.55   $93.60  
  Purchase #7 $191.38   4.315%   $199.638   $199.64   $199.65   $199.60  
  7 purchase totals = $1,015.52       $1,106.7193   $1,106.71   $1,106.70   $1,106.80