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 $129.84   8.742%   $141.1906   $141.19   $141.20   $141.20  
  Purchase #2 $107.33   7.775%   $115.6749   $115.67   $115.65   $115.70  
  Purchase #3 $82.65   8.703%   $89.843   $89.84   $89.85   $89.80  
  Purchase #4 $226.94   13.611%   $257.8288   $257.83   $257.85   $257.80  
  Purchase #5 $161.33   8.363%   $174.822   $174.82   $174.80   $174.80  
  Purchase #6 $27.38   3.641%   $28.3769   $28.38   $28.40   $28.40  
  Purchase #7 $249.37   11.129%   $277.1224   $277.12   $277.10   $277.10  
  7 purchase totals = $984.84       $1,084.8586   $1,084.85   $1,084.85   $1,084.80