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 $169.94   7.678%   $182.988   $182.99   $183.00   $183.00  
  Purchase #2 $95.59   13.506%   $108.5004   $108.50   $108.50   $108.50  
  Purchase #3 $201.34   11.209%   $223.9082   $223.91   $223.90   $223.90  
  Purchase #4 $186.57   4.276%   $194.5477   $194.55   $194.55   $194.50  
  Purchase #5 $194.76   4.142%   $202.827   $202.83   $202.85   $202.80  
  Purchase #6 $248.55   10.782%   $275.3487   $275.35   $275.35   $275.30  
  Purchase #7 $118.52   10.448%   $130.903   $130.90   $130.90   $130.90  
  7 purchase totals = $1,215.27       $1,319.0230   $1,319.03   $1,319.05   $1,318.90