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 $141.47   3.722%   $146.7355   $146.74   $146.75   $146.70  
  Purchase #2 $166.43   3.133%   $171.6443   $171.64   $171.65   $171.60  
  Purchase #3 $159.44   12.210%   $178.9076   $178.91   $178.90   $178.90  
  Purchase #4 $229.53   5.536%   $242.2368   $242.24   $242.25   $242.20  
  Purchase #5 $43.74   10.157%   $48.1827   $48.18   $48.20   $48.20  
  Purchase #6 $153.25   12.782%   $172.8384   $172.84   $172.85   $172.80  
  Purchase #7 $185.28   11.604%   $206.7799   $206.78   $206.80   $206.80  
  7 purchase totals = $1,079.14       $1,167.3252   $1,167.33   $1,167.40   $1,167.20