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 $247.64   5.848%   $262.122   $262.12   $262.10   $262.10  
  Purchase #2 $159.79   7.653%   $172.0187   $172.02   $172.00   $172.00  
  Purchase #3 $147.93   12.669%   $166.6713   $166.67   $166.65   $166.70  
  Purchase #4 $50.26   7.503%   $54.031   $54.03   $54.05   $54.00  
  Purchase #5 $5.44   5.689%   $5.7495   $5.75   $5.75   $5.70  
  Purchase #6 $29.91   3.680%   $31.0107   $31.01   $31.00   $31.00  
  Purchase #7 $231.94   4.190%   $241.6583   $241.66   $241.65   $241.70  
  7 purchase totals = $872.91       $933.2615   $933.26   $933.20   $933.20