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 $173.39   12.275%   $194.6736   $194.67   $194.65   $194.70  
  Purchase #2 $177.84   12.635%   $200.3101   $200.31   $200.30   $200.30  
  Purchase #3 $16.43   4.538%   $17.1756   $17.18   $17.20   $17.20  
  Purchase #4 $57.73   12.704%   $65.064   $65.06   $65.05   $65.10  
  Purchase #5 $192.96   13.352%   $218.724   $218.72   $218.70   $218.70  
  Purchase #6 $239.56   5.594%   $252.961   $252.96   $252.95   $253.00  
  Purchase #7 $118.43   11.776%   $132.3763   $132.38   $132.40   $132.40  
  7 purchase totals = $976.34       $1,081.2846   $1,081.28   $1,081.25   $1,081.40