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 $194.75   6.113%   $206.6551   $206.66   $206.65   $206.70  
  Purchase #2 $181.92   3.779%   $188.7948   $188.79   $188.80   $188.80  
  Purchase #3 $85.43   3.395%   $88.3303   $88.33   $88.35   $88.30  
  Purchase #4 $240.39   12.307%   $269.9748   $269.97   $269.95   $270.00  
  Purchase #5 $48.87   12.257%   $54.86   $54.86   $54.85   $54.90  
  Purchase #6 $118.48   4.132%   $123.3756   $123.38   $123.40   $123.40  
  Purchase #7 $18.51   7.746%   $19.9438   $19.94   $19.95   $19.90  
  7 purchase totals = $888.35       $951.9344   $951.93   $951.95   $952.00