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 $55.46   10.174%   $61.1025   $61.10   $61.10   $61.10  
  Purchase #2 $8.27   3.323%   $8.5448   $8.54   $8.55   $8.50  
  Purchase #3 $237.42   5.686%   $250.9197   $250.92   $250.90   $250.90  
  Purchase #4 $83.77   4.569%   $87.5975   $87.60   $87.60   $87.60  
  Purchase #5 $12.72   7.453%   $13.668   $13.67   $13.65   $13.70  
  Purchase #6 $202.97   9.609%   $222.4734   $222.47   $222.45   $222.50  
  Purchase #7 $141.88   13.230%   $160.6507   $160.65   $160.65   $160.70  
  7 purchase totals = $742.49       $804.9566   $804.95   $804.90   $805.00