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 $235.92   4.184%   $245.7909   $245.79   $245.80   $245.80  
  Purchase #2 $242.74   10.221%   $267.5505   $267.55   $267.55   $267.60  
  Purchase #3 $104.82   6.717%   $111.8608   $111.86   $111.85   $111.90  
  Purchase #4 $75.95   12.173%   $85.1954   $85.20   $85.20   $85.20  
  Purchase #5 $113.58   9.826%   $124.7404   $124.74   $124.75   $124.70  
  Purchase #6 $201.29   6.383%   $214.1383   $214.14   $214.15   $214.10  
  Purchase #7 $179.88   9.466%   $196.9074   $196.91   $196.90   $196.90  
  7 purchase totals = $1,154.18       $1,246.1837   $1,246.19   $1,246.20   $1,246.20