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 $214.36   6.658%   $228.6321   $228.63   $228.65   $228.60  
  Purchase #2 $44.98   9.194%   $49.1155   $49.12   $49.10   $49.10  
  Purchase #3 $51.54   8.603%   $55.974   $55.97   $55.95   $56.00  
  Purchase #4 $14.59   7.446%   $15.6764   $15.68   $15.70   $15.70  
  Purchase #5 $212.85   8.363%   $230.6506   $230.65   $230.65   $230.70  
  Purchase #6 $208.26   11.720%   $232.6681   $232.67   $232.65   $232.70  
  Purchase #7 $228.73   4.269%   $238.4945   $238.49   $238.50   $238.50  
  7 purchase totals = $975.31       $1,051.2112   $1,051.21   $1,051.20   $1,051.30