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 $97.34   11.115%   $108.1593   $108.16   $108.15   $108.20  
  Purchase #2 $171.28   11.519%   $191.0097   $191.01   $191.00   $191.00  
  Purchase #3 $122.29   12.165%   $137.1666   $137.17   $137.15   $137.20  
  Purchase #4 $23.45   11.147%   $26.064   $26.06   $26.05   $26.10  
  Purchase #5 $101.68   7.785%   $109.5958   $109.60   $109.60   $109.60  
  Purchase #6 $84.66   10.553%   $93.5942   $93.59   $93.60   $93.60  
  Purchase #7 $25.40   11.304%   $28.2712   $28.27   $28.25   $28.30  
  7 purchase totals = $626.10       $693.8608   $693.86   $693.80   $694.00