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 $74.38   12.586%   $83.7415   $83.74   $83.75   $83.70  
  Purchase #2 $167.42   3.483%   $173.2512   $173.25   $173.25   $173.30  
  Purchase #3 $128.79   6.230%   $136.8136   $136.81   $136.80   $136.80  
  Purchase #4 $61.75   6.418%   $65.7131   $65.71   $65.70   $65.70  
  Purchase #5 $219.79   9.448%   $240.5558   $240.56   $240.55   $240.60  
  Purchase #6 $25.93   7.501%   $27.875   $27.88   $27.90   $27.90  
  Purchase #7 $211.39   12.145%   $237.0633   $237.06   $237.05   $237.10  
  7 purchase totals = $889.45       $965.0135   $965.01   $965.00   $965.10