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 $113.75   9.852%   $124.9567   $124.96   $124.95   $125.00  
  Purchase #2 $173.99   10.774%   $192.7357   $192.74   $192.75   $192.70  
  Purchase #3 $72.94   8.810%   $79.366   $79.37   $79.35   $79.40  
  Purchase #4 $221.69   8.226%   $239.9262   $239.93   $239.95   $239.90  
  Purchase #5 $190.46   4.489%   $199.0097   $199.01   $199.00   $199.00  
  Purchase #6 $120.29   9.302%   $131.4794   $131.48   $131.50   $131.50  
  Purchase #7 $156.26   7.284%   $167.642   $167.64   $167.65   $167.60  
  7 purchase totals = $1,049.38       $1,135.1157   $1,135.13   $1,135.15   $1,135.10