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 $146.63   3.487%   $151.743   $151.74   $151.75   $151.70  
  Purchase #2 $173.37   11.472%   $193.259   $193.26   $193.25   $193.30  
  Purchase #3 $150.57   13.353%   $170.6756   $170.68   $170.70   $170.70  
  Purchase #4 $97.37   6.851%   $104.0408   $104.04   $104.05   $104.00  
  Purchase #5 $124.51   13.179%   $140.9192   $140.92   $140.90   $140.90  
  Purchase #6 $57.77   5.602%   $61.0063   $61.01   $61.00   $61.00  
  Purchase #7 $183.46   11.636%   $204.8074   $204.81   $204.80   $204.80  
  7 purchase totals = $933.68       $1,026.4513   $1,026.46   $1,026.45   $1,026.40