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 $31.95   13.616%   $36.3003   $36.30   $36.30   $36.30  
  Purchase #2 $88.59   9.266%   $96.7987   $96.80   $96.80   $96.80  
  Purchase #3 $67.57   4.149%   $70.3735   $70.37   $70.35   $70.40  
  Purchase #4 $245.50   11.416%   $273.5263   $273.53   $273.55   $273.50  
  Purchase #5 $38.39   3.207%   $39.6212   $39.62   $39.60   $39.60  
  Purchase #6 $133.75   12.583%   $150.5798   $150.58   $150.60   $150.60  
  Purchase #7 $150.35   8.664%   $163.3763   $163.38   $163.40   $163.40  
  7 purchase totals = $756.10       $830.5761   $830.58   $830.60   $830.60