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 $82.60   6.825%   $88.2375   $88.24   $88.25   $88.20  
  Purchase #2 $145.52   8.524%   $157.9241   $157.92   $157.90   $157.90  
  Purchase #3 $62.83   11.222%   $69.8808   $69.88   $69.90   $69.90  
  Purchase #4 $20.96   7.472%   $22.5261   $22.53   $22.55   $22.50  
  Purchase #5 $49.27   8.846%   $53.6284   $53.63   $53.65   $53.60  
  Purchase #6 $247.25   8.815%   $269.0451   $269.05   $269.05   $269.00  
  Purchase #7 $238.83   6.137%   $253.487   $253.49   $253.50   $253.50  
  7 purchase totals = $847.26       $914.7290   $914.74   $914.80   $914.60