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 $183.95   10.766%   $203.7541   $203.75   $203.75   $203.80  
  Purchase #2 $19.25   4.546%   $20.1251   $20.13   $20.15   $20.10  
  Purchase #3 $220.92   3.467%   $228.5793   $228.58   $228.60   $228.60  
  Purchase #4 $224.52   12.278%   $252.0866   $252.09   $252.10   $252.10  
  Purchase #5 $224.85   5.252%   $236.6591   $236.66   $236.65   $236.70  
  Purchase #6 $94.47   8.734%   $102.721   $102.72   $102.70   $102.70  
  Purchase #7 $23.41   3.237%   $24.1678   $24.17   $24.15   $24.20  
  7 purchase totals = $991.37       $1,068.0930   $1,068.10   $1,068.10   $1,068.20