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 $66.41   10.523%   $73.3983   $73.40   $73.40   $73.40  
  Purchase #2 $135.96   8.738%   $147.8402   $147.84   $147.85   $147.80  
  Purchase #3 $168.32   4.187%   $175.3676   $175.37   $175.35   $175.40  
  Purchase #4 $60.65   3.211%   $62.5975   $62.60   $62.60   $62.60  
  Purchase #5 $235.89   9.852%   $259.1299   $259.13   $259.15   $259.10  
  Purchase #6 $150.73   10.209%   $166.118   $166.12   $166.10   $166.10  
  Purchase #7 $158.64   10.567%   $175.4035   $175.40   $175.40   $175.40  
  7 purchase totals = $976.60       $1,059.8550   $1,059.86   $1,059.85   $1,059.80