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 $150.53   10.621%   $166.5178   $166.52   $166.50   $166.50  
  Purchase #2 $122.33   9.187%   $133.5685   $133.57   $133.55   $133.60  
  Purchase #3 $56.56   3.587%   $58.5888   $58.59   $58.60   $58.60  
  Purchase #4 $52.38   4.384%   $54.6763   $54.68   $54.70   $54.70  
  Purchase #5 $37.41   9.681%   $41.0317   $41.03   $41.05   $41.00  
  Purchase #6 $123.39   9.229%   $134.7777   $134.78   $134.80   $134.80  
  Purchase #7 $195.76   6.323%   $208.1379   $208.14   $208.15   $208.10  
  7 purchase totals = $738.36       $797.2987   $797.31   $797.35   $797.30