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 $130.91   8.761%   $142.379   $142.38   $142.40   $142.40  
  Purchase #2 $97.29   10.404%   $107.4121   $107.41   $107.40   $107.40  
  Purchase #3 $25.75   7.402%   $27.656   $27.66   $27.65   $27.70  
  Purchase #4 $139.44   5.508%   $147.1204   $147.12   $147.10   $147.10  
  Purchase #5 $167.81   7.520%   $180.4293   $180.43   $180.45   $180.40  
  Purchase #6 $203.29   13.740%   $231.222   $231.22   $231.20   $231.20  
  Purchase #7 $70.54   10.639%   $78.0448   $78.04   $78.05   $78.00  
  7 purchase totals = $835.03       $914.2636   $914.26   $914.25   $914.20