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 $224.69   9.567%   $246.1861   $246.19   $246.20   $246.20  
  Purchase #2 $103.64   6.861%   $110.7507   $110.75   $110.75   $110.80  
  Purchase #3 $155.80   8.852%   $169.5914   $169.59   $169.60   $169.60  
  Purchase #4 $71.29   12.462%   $80.1742   $80.17   $80.15   $80.20  
  Purchase #5 $206.39   4.833%   $216.3648   $216.36   $216.35   $216.40  
  Purchase #6 $120.43   3.200%   $124.2838   $124.28   $124.30   $124.30  
  Purchase #7 $106.82   12.299%   $119.9578   $119.96   $119.95   $120.00  
  7 purchase totals = $989.06       $1,067.3088   $1,067.30   $1,067.30   $1,067.50