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 $218.65   12.589%   $246.1758   $246.18   $246.20   $246.20  
  Purchase #2 $17.62   6.675%   $18.7961   $18.80   $18.80   $18.80  
  Purchase #3 $120.98   7.759%   $130.3668   $130.37   $130.35   $130.40  
  Purchase #4 $156.47   9.494%   $171.3253   $171.33   $171.35   $171.30  
  Purchase #5 $188.96   3.587%   $195.738   $195.74   $195.75   $195.70  
  Purchase #6 $200.25   12.421%   $225.1231   $225.12   $225.10   $225.10  
  Purchase #7 $192.72   8.313%   $208.7408   $208.74   $208.75   $208.70  
  7 purchase totals = $1,095.65       $1,196.2659   $1,196.28   $1,196.30   $1,196.20