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 $47.41   7.658%   $51.0407   $51.04   $51.05   $51.00  
  Purchase #2 $124.40   13.176%   $140.7909   $140.79   $140.80   $140.80  
  Purchase #3 $147.65   4.733%   $154.6383   $154.64   $154.65   $154.60  
  Purchase #4 $211.92   4.252%   $220.9308   $220.93   $220.95   $220.90  
  Purchase #5 $204.78   4.768%   $214.5439   $214.54   $214.55   $214.50  
  Purchase #6 $181.63   11.125%   $201.8363   $201.84   $201.85   $201.80  
  Purchase #7 $59.99   7.690%   $64.6032   $64.60   $64.60   $64.60  
  7 purchase totals = $977.78       $1,048.3841   $1,048.38   $1,048.45   $1,048.20