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 $201.36   11.274%   $224.0613   $224.06   $224.05   $224.10  
  Purchase #2 $183.47   12.321%   $206.0753   $206.08   $206.10   $206.10  
  Purchase #3 $149.98   12.122%   $168.1606   $168.16   $168.15   $168.20  
  Purchase #4 $111.96   7.494%   $120.3503   $120.35   $120.35   $120.40  
  Purchase #5 $124.41   9.147%   $135.7898   $135.79   $135.80   $135.80  
  Purchase #6 $157.40   5.849%   $166.6063   $166.61   $166.60   $166.60  
  Purchase #7 $203.32   8.274%   $220.1427   $220.14   $220.15   $220.10  
  7 purchase totals = $1,131.90       $1,241.1863   $1,241.19   $1,241.20   $1,241.30