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 $64.34   7.635%   $69.2524   $69.25   $69.25   $69.30  
  Purchase #2 $110.44   9.752%   $121.2101   $121.21   $121.20   $121.20  
  Purchase #3 $219.42   4.280%   $228.8112   $228.81   $228.80   $228.80  
  Purchase #4 $186.68   13.738%   $212.3261   $212.33   $212.35   $212.30  
  Purchase #5 $95.80   10.524%   $105.882   $105.88   $105.90   $105.90  
  Purchase #6 $215.26   8.143%   $232.7886   $232.79   $232.80   $232.80  
  Purchase #7 $43.58   5.609%   $46.0244   $46.02   $46.00   $46.00  
  7 purchase totals = $935.52       $1,016.2948   $1,016.29   $1,016.30   $1,016.30