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 $174.87   10.534%   $193.2908   $193.29   $193.30   $193.30  
  Purchase #2 $149.50   4.575%   $156.3396   $156.34   $156.35   $156.30  
  Purchase #3 $229.87   3.288%   $237.4281   $237.43   $237.45   $237.40  
  Purchase #4 $218.55   8.623%   $237.3956   $237.40   $237.40   $237.40  
  Purchase #5 $241.54   3.782%   $250.675   $250.68   $250.70   $250.70  
  Purchase #6 $148.70   4.720%   $155.7186   $155.72   $155.70   $155.70  
  Purchase #7 $96.38   6.426%   $102.5734   $102.57   $102.55   $102.60  
  7 purchase totals = $1,259.41       $1,333.4211   $1,333.43   $1,333.45   $1,333.40