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 $93.56   10.158%   $103.0638   $103.06   $103.05   $103.10  
  Purchase #2 $137.45   7.258%   $147.4261   $147.43   $147.45   $147.40  
  Purchase #3 $164.89   11.387%   $183.666   $183.67   $183.65   $183.70  
  Purchase #4 $200.94   11.448%   $223.9436   $223.94   $223.95   $223.90  
  Purchase #5 $188.53   6.577%   $200.9296   $200.93   $200.95   $200.90  
  Purchase #6 $132.31   12.743%   $149.1703   $149.17   $149.15   $149.20  
  Purchase #7 $96.68   8.513%   $104.9104   $104.91   $104.90   $104.90  
  7 purchase totals = $1,014.36       $1,113.1098   $1,113.11   $1,113.10   $1,113.10