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 $54.87   10.170%   $60.4503   $60.45   $60.45   $60.50  
  Purchase #2 $192.56   5.608%   $203.3588   $203.36   $203.35   $203.40  
  Purchase #3 $71.80   7.755%   $77.3681   $77.37   $77.35   $77.40  
  Purchase #4 $210.92   10.433%   $232.9253   $232.93   $232.95   $232.90  
  Purchase #5 $67.40   5.668%   $71.2202   $71.22   $71.20   $71.20  
  Purchase #6 $217.79   3.326%   $225.0337   $225.03   $225.05   $225.00  
  Purchase #7 $223.34   4.426%   $233.225   $233.23   $233.25   $233.20  
  7 purchase totals = $1,038.68       $1,103.5814   $1,103.59   $1,103.60   $1,103.60