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 $126.83   12.402%   $142.5595   $142.56   $142.55   $142.60  
  Purchase #2 $76.62   10.432%   $84.613   $84.61   $84.60   $84.60  
  Purchase #3 $169.39   3.157%   $174.7376   $174.74   $174.75   $174.70  
  Purchase #4 $240.52   13.179%   $272.2181   $272.22   $272.20   $272.20  
  Purchase #5 $185.32   3.279%   $191.3966   $191.40   $191.40   $191.40  
  Purchase #6 $153.36   5.105%   $161.189   $161.19   $161.20   $161.20  
  Purchase #7 $108.79   11.679%   $121.4956   $121.50   $121.50   $121.50  
  7 purchase totals = $1,060.83       $1,148.2094   $1,148.22   $1,148.20   $1,148.20