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 $220.77   11.853%   $246.9379   $246.94   $246.95   $246.90  
  Purchase #2 $233.66   12.835%   $263.6503   $263.65   $263.65   $263.70  
  Purchase #3 $62.32   7.829%   $67.199   $67.20   $67.20   $67.20  
  Purchase #4 $84.31   5.758%   $89.1646   $89.16   $89.15   $89.20  
  Purchase #5 $30.28   13.481%   $34.362   $34.36   $34.35   $34.40  
  Purchase #6 $110.37   11.237%   $122.7723   $122.77   $122.75   $122.80  
  Purchase #7 $183.57   4.610%   $192.0326   $192.03   $192.05   $192.00  
  7 purchase totals = $925.28       $1,016.1187   $1,016.11   $1,016.10   $1,016.20