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 $218.93   10.174%   $241.2039   $241.20   $241.20   $241.20  
  Purchase #2 $126.43   3.753%   $131.1749   $131.17   $131.15   $131.20  
  Purchase #3 $153.79   9.327%   $168.134   $168.13   $168.15   $168.10  
  Purchase #4 $161.73   9.402%   $176.9359   $176.94   $176.95   $176.90  
  Purchase #5 $60.40   8.640%   $65.6186   $65.62   $65.60   $65.60  
  Purchase #6 $156.68   6.564%   $166.9645   $166.96   $166.95   $167.00  
  Purchase #7 $239.45   7.611%   $257.6745   $257.67   $257.65   $257.70  
  7 purchase totals = $1,117.41       $1,207.7063   $1,207.69   $1,207.65   $1,207.70