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 $72.53   3.653%   $75.1795   $75.18   $75.20   $75.20  
  Purchase #2 $56.97   9.153%   $62.1845   $62.18   $62.20   $62.20  
  Purchase #3 $228.59   11.167%   $254.1166   $254.12   $254.10   $254.10  
  Purchase #4 $183.81   11.724%   $205.3599   $205.36   $205.35   $205.40  
  Purchase #5 $158.40   9.223%   $173.0092   $173.01   $173.00   $173.00  
  Purchase #6 $226.85   11.191%   $252.2368   $252.24   $252.25   $252.20  
  Purchase #7 $63.39   12.507%   $71.3182   $71.32   $71.30   $71.30  
  7 purchase totals = $990.54       $1,093.4047   $1,093.41   $1,093.40   $1,093.40