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 $181.81   9.290%   $198.7001   $198.70   $198.70   $198.70  
  Purchase #2 $9.57   6.743%   $10.2153   $10.22   $10.20   $10.20  
  Purchase #3 $49.53   10.752%   $54.8555   $54.86   $54.85   $54.90  
  Purchase #4 $246.64   8.448%   $267.4761   $267.48   $267.50   $267.50  
  Purchase #5 $111.41   13.258%   $126.1807   $126.18   $126.20   $126.20  
  Purchase #6 $165.73   12.622%   $186.6484   $186.65   $186.65   $186.60  
  Purchase #7 $145.50   4.121%   $151.4961   $151.50   $151.50   $151.50  
  7 purchase totals = $910.19       $995.5722   $995.59   $995.60   $995.60