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 $210.98   13.489%   $239.4391   $239.44   $239.45   $239.40  
  Purchase #2 $113.91   5.112%   $119.7331   $119.73   $119.75   $119.70  
  Purchase #3 $190.43   3.373%   $196.8532   $196.85   $196.85   $196.90  
  Purchase #4 $116.94   6.183%   $124.1704   $124.17   $124.15   $124.20  
  Purchase #5 $166.69   3.774%   $172.9809   $172.98   $173.00   $173.00  
  Purchase #6 $131.56   13.686%   $149.5653   $149.57   $149.55   $149.60  
  Purchase #7 $246.82   5.173%   $259.588   $259.59   $259.60   $259.60  
  7 purchase totals = $1,177.33       $1,262.3300   $1,262.33   $1,262.35   $1,262.40