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 $232.26   10.874%   $257.516   $257.52   $257.50   $257.50  
  Purchase #2 $172.48   4.190%   $179.7069   $179.71   $179.70   $179.70  
  Purchase #3 $57.77   7.423%   $62.0583   $62.06   $62.05   $62.10  
  Purchase #4 $109.41   6.672%   $116.7098   $116.71   $116.70   $116.70  
  Purchase #5 $214.73   4.861%   $225.168   $225.17   $225.15   $225.20  
  Purchase #6 $92.94   4.116%   $96.7654   $96.77   $96.75   $96.80  
  Purchase #7 $74.50   3.805%   $77.3347   $77.33   $77.35   $77.30  
  7 purchase totals = $954.09       $1,015.2591   $1,015.27   $1,015.20   $1,015.30