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 $214.61   12.616%   $241.6852   $241.69   $241.70   $241.70  
  Purchase #2 $95.52   9.809%   $104.8896   $104.89   $104.90   $104.90  
  Purchase #3 $23.50   7.349%   $25.227   $25.23   $25.25   $25.20  
  Purchase #4 $96.71   13.167%   $109.4438   $109.44   $109.45   $109.40  
  Purchase #5 $186.45   8.835%   $202.9229   $202.92   $202.90   $202.90  
  Purchase #6 $51.31   11.234%   $57.0742   $57.07   $57.05   $57.10  
  Purchase #7 $193.25   8.710%   $210.0821   $210.08   $210.10   $210.10  
  7 purchase totals = $861.35       $951.3248   $951.32   $951.35   $951.30