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 $55.34   11.861%   $61.9039   $61.90   $61.90   $61.90  
  Purchase #2 $154.57   4.788%   $161.9708   $161.97   $161.95   $162.00  
  Purchase #3 $80.60   6.675%   $85.9801   $85.98   $86.00   $86.00  
  Purchase #4 $163.82   6.784%   $174.9335   $174.93   $174.95   $174.90  
  Purchase #5 $157.34   13.687%   $178.8751   $178.88   $178.90   $178.90  
  Purchase #6 $121.40   9.841%   $133.347   $133.35   $133.35   $133.30  
  Purchase #7 $203.58   8.294%   $220.4649   $220.46   $220.45   $220.50  
  7 purchase totals = $936.65       $1,017.4753   $1,017.47   $1,017.50   $1,017.50