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 $212.84   8.432%   $230.7867   $230.79   $230.80   $230.80  
  Purchase #2 $63.64   9.538%   $69.71   $69.71   $69.70   $69.70  
  Purchase #3 $42.84   4.431%   $44.7382   $44.74   $44.75   $44.70  
  Purchase #4 $150.93   9.390%   $165.1023   $165.10   $165.10   $165.10  
  Purchase #5 $239.89   6.302%   $255.0079   $255.01   $255.00   $255.00  
  Purchase #6 $61.26   7.340%   $65.7565   $65.76   $65.75   $65.80  
  Purchase #7 $106.31   12.798%   $119.9156   $119.92   $119.90   $119.90  
  7 purchase totals = $877.71       $951.0172   $951.03   $951.00   $951.00