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 $169.43   7.502%   $182.1406   $182.14   $182.15   $182.10  
  Purchase #2 $151.56   13.606%   $172.1813   $172.18   $172.20   $172.20  
  Purchase #3 $57.88   11.402%   $64.4795   $64.48   $64.50   $64.50  
  Purchase #4 $161.83   12.427%   $181.9406   $181.94   $181.95   $181.90  
  Purchase #5 $179.66   11.285%   $199.9346   $199.93   $199.95   $199.90  
  Purchase #6 $203.56   3.819%   $211.334   $211.33   $211.35   $211.30  
  Purchase #7 $219.94   12.679%   $247.8262   $247.83   $247.85   $247.80  
  7 purchase totals = $1,143.86       $1,259.8368   $1,259.83   $1,259.95   $1,259.70