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 $46.41   8.426%   $50.3205   $50.32   $50.30   $50.30  
  Purchase #2 $152.92   12.310%   $171.7445   $171.74   $171.75   $171.70  
  Purchase #3 $169.44   3.780%   $175.8448   $175.84   $175.85   $175.80  
  Purchase #4 $194.69   7.869%   $210.0102   $210.01   $210.00   $210.00  
  Purchase #5 $158.64   9.713%   $174.0487   $174.05   $174.05   $174.00  
  Purchase #6 $157.44   12.266%   $176.7516   $176.75   $176.75   $176.80  
  Purchase #7 $72.54   5.521%   $76.5449   $76.54   $76.55   $76.50  
  7 purchase totals = $952.08       $1,035.2652   $1,035.25   $1,035.25   $1,035.10