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 $43.56   11.716%   $48.6635   $48.66   $48.65   $48.70  
  Purchase #2 $207.70   13.732%   $236.2214   $236.22   $236.20   $236.20  
  Purchase #3 $50.65   13.380%   $57.427   $57.43   $57.45   $57.40  
  Purchase #4 $214.83   8.442%   $232.9659   $232.97   $232.95   $233.00  
  Purchase #5 $235.75   5.424%   $248.5371   $248.54   $248.55   $248.50  
  Purchase #6 $141.83   8.410%   $153.7579   $153.76   $153.75   $153.80  
  Purchase #7 $61.53   7.464%   $66.1226   $66.12   $66.10   $66.10  
  7 purchase totals = $955.85       $1,043.6954   $1,043.70   $1,043.65   $1,043.70