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 $140.92   6.431%   $149.9826   $149.98   $150.00   $150.00  
  Purchase #2 $167.26   13.657%   $190.1027   $190.10   $190.10   $190.10  
  Purchase #3 $60.59   12.567%   $68.2043   $68.20   $68.20   $68.20  
  Purchase #4 $232.33   11.852%   $259.8658   $259.87   $259.85   $259.90  
  Purchase #5 $6.94   9.308%   $7.586   $7.59   $7.60   $7.60  
  Purchase #6 $211.32   11.528%   $235.681   $235.68   $235.70   $235.70  
  Purchase #7 $12.33   6.825%   $13.1715   $13.17   $13.15   $13.20  
  7 purchase totals = $831.69       $924.5939   $924.59   $924.60   $924.70