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 $63.28   12.723%   $71.3311   $71.33   $71.35   $71.30  
  Purchase #2 $195.84   13.194%   $221.6791   $221.68   $221.70   $221.70  
  Purchase #3 $166.94   5.230%   $175.671   $175.67   $175.65   $175.70  
  Purchase #4 $130.69   12.197%   $146.6303   $146.63   $146.65   $146.60  
  Purchase #5 $215.58   4.590%   $225.4751   $225.48   $225.50   $225.50  
  Purchase #6 $33.96   7.695%   $36.5732   $36.57   $36.55   $36.60  
  Purchase #7 $121.60   7.544%   $130.7735   $130.77   $130.75   $130.80  
  7 purchase totals = $927.89       $1,008.1333   $1,008.13   $1,008.15   $1,008.20