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 $94.31   11.111%   $104.7888   $104.79   $104.80   $104.80  
  Purchase #2 $198.49   5.122%   $208.6567   $208.66   $208.65   $208.70  
  Purchase #3 $242.39   6.111%   $257.2025   $257.20   $257.20   $257.20  
  Purchase #4 $46.69   3.763%   $48.4469   $48.45   $48.45   $48.40  
  Purchase #5 $241.29   10.376%   $266.3263   $266.33   $266.35   $266.30  
  Purchase #6 $67.70   7.714%   $72.9224   $72.92   $72.90   $72.90  
  Purchase #7 $80.82   8.202%   $87.4489   $87.45   $87.45   $87.40  
  7 purchase totals = $971.69       $1,045.7925   $1,045.80   $1,045.80   $1,045.70