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 $58.49   12.565%   $65.8393   $65.84   $65.85   $65.80  
  Purchase #2 $226.64   4.842%   $237.6139   $237.61   $237.60   $237.60  
  Purchase #3 $100.66   3.585%   $104.2687   $104.27   $104.25   $104.30  
  Purchase #4 $35.43   10.809%   $39.2596   $39.26   $39.25   $39.30  
  Purchase #5 $126.27   12.797%   $142.4288   $142.43   $142.45   $142.40  
  Purchase #6 $211.89   7.322%   $227.4046   $227.40   $227.40   $227.40  
  Purchase #7 $23.82   6.524%   $25.374   $25.37   $25.35   $25.40  
  7 purchase totals = $783.20       $842.1889   $842.18   $842.15   $842.20