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 $118.63   13.594%   $134.7566   $134.76   $134.75   $134.80  
  Purchase #2 $240.88   12.122%   $270.0795   $270.08   $270.10   $270.10  
  Purchase #3 $58.77   6.668%   $62.6888   $62.69   $62.70   $62.70  
  Purchase #4 $60.47   9.148%   $66.0018   $66.00   $66.00   $66.00  
  Purchase #5 $240.29   7.270%   $257.7591   $257.76   $257.75   $257.80  
  Purchase #6 $172.48   6.237%   $183.2376   $183.24   $183.25   $183.20  
  Purchase #7 $68.44   9.583%   $74.9986   $75.00   $75.00   $75.00  
  7 purchase totals = $959.96       $1,049.5220   $1,049.53   $1,049.55   $1,049.60