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 $197.44   6.380%   $210.0367   $210.04   $210.05   $210.00  
  Purchase #2 $175.70   8.452%   $190.5502   $190.55   $190.55   $190.60  
  Purchase #3 $91.45   5.439%   $96.424   $96.42   $96.40   $96.40  
  Purchase #4 $13.38   11.222%   $14.8815   $14.88   $14.90   $14.90  
  Purchase #5 $69.34   6.867%   $74.1016   $74.10   $74.10   $74.10  
  Purchase #6 $60.35   8.559%   $65.5154   $65.52   $65.50   $65.50  
  Purchase #7 $41.59   7.241%   $44.6015   $44.60   $44.60   $44.60  
  7 purchase totals = $649.25       $696.1109   $696.11   $696.10   $696.10