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 $62.74   13.542%   $71.2363   $71.24   $71.25   $71.20  
  Purchase #2 $231.70   3.279%   $239.2974   $239.30   $239.30   $239.30  
  Purchase #3 $179.87   13.170%   $203.5589   $203.56   $203.55   $203.60  
  Purchase #4 $220.65   11.810%   $246.7088   $246.71   $246.70   $246.70  
  Purchase #5 $171.58   12.273%   $192.638   $192.64   $192.65   $192.60  
  Purchase #6 $247.36   11.827%   $276.6153   $276.62   $276.60   $276.60  
  Purchase #7 $101.63   11.507%   $113.3246   $113.32   $113.30   $113.30  
  7 purchase totals = $1,215.53       $1,343.3793   $1,343.39   $1,343.35   $1,343.30