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 $180.61   8.652%   $196.2364   $196.24   $196.25   $196.20  
  Purchase #2 $225.37   4.385%   $235.2525   $235.25   $235.25   $235.30  
  Purchase #3 $227.46   11.709%   $254.0933   $254.09   $254.10   $254.10  
  Purchase #4 $186.52   8.650%   $202.654   $202.65   $202.65   $202.70  
  Purchase #5 $153.96   7.486%   $165.4854   $165.49   $165.50   $165.50  
  Purchase #6 $228.52   13.642%   $259.6947   $259.69   $259.70   $259.70  
  Purchase #7 $39.34   12.131%   $44.1123   $44.11   $44.10   $44.10  
  7 purchase totals = $1,241.78       $1,357.5286   $1,357.52   $1,357.55   $1,357.60