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 $222.97   4.478%   $232.9546   $232.95   $232.95   $233.00  
  Purchase #2 $60.70   8.684%   $65.9712   $65.97   $65.95   $66.00  
  Purchase #3 $76.94   13.715%   $87.4923   $87.49   $87.50   $87.50  
  Purchase #4 $206.49   10.456%   $228.0806   $228.08   $228.10   $228.10  
  Purchase #5 $162.25   11.544%   $180.9801   $180.98   $181.00   $181.00  
  Purchase #6 $246.71   12.575%   $277.7338   $277.73   $277.75   $277.70  
  Purchase #7 $26.42   13.580%   $30.0078   $30.01   $30.00   $30.00  
  7 purchase totals = $1,002.48       $1,103.2204   $1,103.21   $1,103.25   $1,103.30