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 $127.89   5.568%   $135.0109   $135.01   $135.00   $135.00  
  Purchase #2 $186.69   4.608%   $195.2927   $195.29   $195.30   $195.30  
  Purchase #3 $241.25   11.439%   $268.8466   $268.85   $268.85   $268.80  
  Purchase #4 $122.83   9.466%   $134.4571   $134.46   $134.45   $134.50  
  Purchase #5 $205.29   11.605%   $229.1139   $229.11   $229.10   $229.10  
  Purchase #6 $37.38   5.206%   $39.326   $39.33   $39.35   $39.30  
  Purchase #7 $147.85   11.481%   $164.8247   $164.82   $164.80   $164.80  
  7 purchase totals = $1,069.18       $1,166.8719   $1,166.87   $1,166.85   $1,166.80