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 $62.61   6.211%   $66.4987   $66.50   $66.50   $66.50  
  Purchase #2 $226.29   12.299%   $254.1214   $254.12   $254.10   $254.10  
  Purchase #3 $244.64   13.314%   $277.2114   $277.21   $277.20   $277.20  
  Purchase #4 $246.74   7.447%   $265.1147   $265.11   $265.10   $265.10  
  Purchase #5 $60.32   4.668%   $63.1357   $63.14   $63.15   $63.10  
  Purchase #6 $99.79   6.834%   $106.6096   $106.61   $106.60   $106.60  
  Purchase #7 $71.97   4.600%   $75.2806   $75.28   $75.30   $75.30  
  7 purchase totals = $1,012.36       $1,107.9721   $1,107.97   $1,107.95   $1,107.90