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 $85.61   8.604%   $92.9759   $92.98   $93.00   $93.00  
  Purchase #2 $115.93   5.122%   $121.8679   $121.87   $121.85   $121.90  
  Purchase #3 $246.53   3.424%   $254.9712   $254.97   $254.95   $255.00  
  Purchase #4 $18.50   11.122%   $20.5576   $20.56   $20.55   $20.60  
  Purchase #5 $75.85   13.618%   $86.1793   $86.18   $86.20   $86.20  
  Purchase #6 $86.87   6.616%   $92.6173   $92.62   $92.60   $92.60  
  Purchase #7 $168.92   5.572%   $178.3322   $178.33   $178.35   $178.30  
  7 purchase totals = $798.21       $847.5014   $847.51   $847.50   $847.60