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 $214.69   6.511%   $228.6685   $228.67   $228.65   $228.70  
  Purchase #2 $215.65   5.229%   $226.9263   $226.93   $226.95   $226.90  
  Purchase #3 $55.27   11.431%   $61.5879   $61.59   $61.60   $61.60  
  Purchase #4 $198.67   13.242%   $224.9779   $224.98   $225.00   $225.00  
  Purchase #5 $90.95   8.174%   $98.3843   $98.38   $98.40   $98.40  
  Purchase #6 $72.91   6.502%   $77.6506   $77.65   $77.65   $77.70  
  Purchase #7 $97.98   4.413%   $102.3039   $102.30   $102.30   $102.30  
  7 purchase totals = $946.12       $1,020.4994   $1,020.50   $1,020.55   $1,020.60