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 $178.67   8.646%   $194.1178   $194.12   $194.10   $194.10  
  Purchase #2 $246.33   8.342%   $266.8788   $266.88   $266.90   $266.90  
  Purchase #3 $103.32   6.331%   $109.8612   $109.86   $109.85   $109.90  
  Purchase #4 $81.36   13.629%   $92.4486   $92.45   $92.45   $92.40  
  Purchase #5 $195.38   11.283%   $217.4247   $217.42   $217.40   $217.40  
  Purchase #6 $237.96   13.574%   $270.2607   $270.26   $270.25   $270.30  
  Purchase #7 $162.56   11.776%   $181.7031   $181.70   $181.70   $181.70  
  7 purchase totals = $1,205.58       $1,332.6949   $1,332.69   $1,332.65   $1,332.70