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 $52.45   13.595%   $59.5806   $59.58   $59.60   $59.60  
  Purchase #2 $54.60   13.806%   $62.1381   $62.14   $62.15   $62.10  
  Purchase #3 $233.89   12.560%   $263.2666   $263.27   $263.25   $263.30  
  Purchase #4 $220.70   7.396%   $237.023   $237.02   $237.00   $237.00  
  Purchase #5 $195.65   3.302%   $202.1104   $202.11   $202.10   $202.10  
  Purchase #6 $177.36   12.610%   $199.7251   $199.73   $199.75   $199.70  
  Purchase #7 $226.96   7.353%   $243.6484   $243.65   $243.65   $243.60  
  7 purchase totals = $1,161.61       $1,267.4922   $1,267.50   $1,267.50   $1,267.40