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 $60.83   11.374%   $67.7488   $67.75   $67.75   $67.70  
  Purchase #2 $216.79   13.185%   $245.3738   $245.37   $245.35   $245.40  
  Purchase #3 $76.27   5.830%   $80.7165   $80.72   $80.70   $80.70  
  Purchase #4 $218.61   8.441%   $237.0629   $237.06   $237.05   $237.10  
  Purchase #5 $216.29   10.506%   $239.0134   $239.01   $239.00   $239.00  
  Purchase #6 $232.58   13.408%   $263.7643   $263.76   $263.75   $263.80  
  Purchase #7 $162.92   10.260%   $179.6356   $179.64   $179.65   $179.60  
  7 purchase totals = $1,184.29       $1,313.3153   $1,313.31   $1,313.25   $1,313.30