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 $61.47   5.751%   $65.0051   $65.01   $65.00   $65.00  
  Purchase #2 $181.62   6.429%   $193.2963   $193.30   $193.30   $193.30  
  Purchase #3 $242.47   5.222%   $255.1318   $255.13   $255.15   $255.10  
  Purchase #4 $116.81   4.310%   $121.8445   $121.84   $121.85   $121.80  
  Purchase #5 $38.88   7.150%   $41.6599   $41.66   $41.65   $41.70  
  Purchase #6 $39.36   13.627%   $44.7236   $44.72   $44.70   $44.70  
  Purchase #7 $146.81   9.251%   $160.3914   $160.39   $160.40   $160.40  
  7 purchase totals = $827.42       $882.0526   $882.05   $882.05   $882.00