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 $244.33   9.369%   $267.2213   $267.22   $267.20   $267.20  
  Purchase #2 $81.74   13.605%   $92.8607   $92.86   $92.85   $92.90  
  Purchase #3 $120.53   4.374%   $125.802   $125.80   $125.80   $125.80  
  Purchase #4 $167.95   11.295%   $186.92   $186.92   $186.90   $186.90  
  Purchase #5 $172.48   7.233%   $184.9555   $184.96   $184.95   $185.00  
  Purchase #6 $88.69   5.260%   $93.3551   $93.36   $93.35   $93.40  
  Purchase #7 $65.95   12.346%   $74.0922   $74.09   $74.10   $74.10  
  7 purchase totals = $941.67       $1,025.2068   $1,025.21   $1,025.15   $1,025.30