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 $143.97   5.372%   $151.7041   $151.70   $151.70   $151.70  
  Purchase #2 $93.37   13.137%   $105.636   $105.64   $105.65   $105.60  
  Purchase #3 $75.65   4.812%   $79.2903   $79.29   $79.30   $79.30  
  Purchase #4 $22.68   13.759%   $25.8005   $25.80   $25.80   $25.80  
  Purchase #5 $131.54   7.512%   $141.4213   $141.42   $141.40   $141.40  
  Purchase #6 $154.26   9.587%   $169.0489   $169.05   $169.05   $169.00  
  Purchase #7 $82.66   13.228%   $93.5943   $93.59   $93.60   $93.60  
  7 purchase totals = $704.13       $766.4954   $766.49   $766.50   $766.40