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 $96.81   7.762%   $104.3244   $104.32   $104.30   $104.30  
  Purchase #2 $146.49   13.344%   $166.0376   $166.04   $166.05   $166.00  
  Purchase #3 $202.56   12.480%   $227.8395   $227.84   $227.85   $227.80  
  Purchase #4 $70.64   5.584%   $74.5845   $74.58   $74.60   $74.60  
  Purchase #5 $56.62   11.824%   $63.3147   $63.31   $63.30   $63.30  
  Purchase #6 $153.52   8.712%   $166.8947   $166.89   $166.90   $166.90  
  Purchase #7 $183.83   9.816%   $201.8748   $201.87   $201.85   $201.90  
  7 purchase totals = $910.47       $1,004.8702   $1,004.85   $1,004.85   $1,004.80