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 $61.34   12.662%   $69.1069   $69.11   $69.10   $69.10  
  Purchase #2 $70.99   5.162%   $74.6545   $74.65   $74.65   $74.70  
  Purchase #3 $45.82   12.163%   $51.3931   $51.39   $51.40   $51.40  
  Purchase #4 $137.70   13.811%   $156.7177   $156.72   $156.70   $156.70  
  Purchase #5 $211.49   3.359%   $218.5939   $218.59   $218.60   $218.60  
  Purchase #6 $156.82   13.218%   $177.5485   $177.55   $177.55   $177.50  
  Purchase #7 $100.58   4.281%   $104.8858   $104.89   $104.90   $104.90  
  7 purchase totals = $784.74       $852.9004   $852.90   $852.90   $852.90