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 $231.81   13.481%   $263.0603   $263.06   $263.05   $263.10  
  Purchase #2 $54.73   8.565%   $59.4176   $59.42   $59.40   $59.40  
  Purchase #3 $166.55   4.667%   $174.3229   $174.32   $174.30   $174.30  
  Purchase #4 $232.60   4.526%   $243.1275   $243.13   $243.15   $243.10  
  Purchase #5 $192.87   11.279%   $214.6238   $214.62   $214.60   $214.60  
  Purchase #6 $134.78   10.349%   $148.7284   $148.73   $148.75   $148.70  
  Purchase #7 $220.80   6.870%   $235.969   $235.97   $235.95   $236.00  
  7 purchase totals = $1,234.14       $1,339.2495   $1,339.25   $1,339.20   $1,339.20