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 $89.87   5.850%   $95.1274   $95.13   $95.15   $95.10  
  Purchase #2 $125.84   13.484%   $142.8083   $142.81   $142.80   $142.80  
  Purchase #3 $172.62   12.572%   $194.3218   $194.32   $194.30   $194.30  
  Purchase #4 $97.71   9.507%   $106.9993   $107.00   $107.00   $107.00  
  Purchase #5 $219.45   8.611%   $238.3468   $238.35   $238.35   $238.30  
  Purchase #6 $246.86   8.762%   $268.4899   $268.49   $268.50   $268.50  
  Purchase #7 $237.25   11.868%   $265.4068   $265.41   $265.40   $265.40  
  7 purchase totals = $1,189.60       $1,311.5003   $1,311.51   $1,311.50   $1,311.40