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 $180.98   11.619%   $202.0081   $202.01   $202.00   $202.00  
  Purchase #2 $153.70   7.564%   $165.3259   $165.33   $165.35   $165.30  
  Purchase #3 $124.36   7.193%   $133.3052   $133.31   $133.30   $133.30  
  Purchase #4 $7.62   13.419%   $8.6425   $8.64   $8.65   $8.60  
  Purchase #5 $202.35   3.554%   $209.5415   $209.54   $209.55   $209.50  
  Purchase #6 $233.73   5.505%   $246.5968   $246.60   $246.60   $246.60  
  Purchase #7 $22.47   7.647%   $24.1883   $24.19   $24.20   $24.20  
  7 purchase totals = $925.21       $989.6083   $989.62   $989.65   $989.50