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 $150.96   10.144%   $166.2734   $166.27   $166.25   $166.30  
  Purchase #2 $111.94   7.548%   $120.3892   $120.39   $120.40   $120.40  
  Purchase #3 $43.43   8.253%   $47.0143   $47.01   $47.00   $47.00  
  Purchase #4 $200.86   7.212%   $215.346   $215.35   $215.35   $215.30  
  Purchase #5 $239.28   6.276%   $254.2972   $254.30   $254.30   $254.30  
  Purchase #6 $100.93   11.346%   $112.3815   $112.38   $112.40   $112.40  
  Purchase #7 $110.81   4.864%   $116.1998   $116.20   $116.20   $116.20  
  7 purchase totals = $958.21       $1,031.9014   $1,031.90   $1,031.90   $1,031.90