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 $235.66   11.557%   $262.8952   $262.90   $262.90   $262.90  
  Purchase #2 $111.86   13.282%   $126.7172   $126.72   $126.70   $126.70  
  Purchase #3 $197.75   3.602%   $204.873   $204.87   $204.85   $204.90  
  Purchase #4 $27.71   13.821%   $31.5398   $31.54   $31.55   $31.50  
  Purchase #5 $183.53   8.849%   $199.7706   $199.77   $199.75   $199.80  
  Purchase #6 $165.58   9.623%   $181.5138   $181.51   $181.50   $181.50  
  Purchase #7 $58.25   8.412%   $63.15   $63.15   $63.15   $63.20  
  7 purchase totals = $980.34       $1,070.4596   $1,070.46   $1,070.40   $1,070.50