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 $58.34   12.510%   $65.6383   $65.64   $65.65   $65.60  
  Purchase #2 $126.72   4.599%   $132.5479   $132.55   $132.55   $132.50  
  Purchase #3 $221.49   8.364%   $240.0154   $240.02   $240.00   $240.00  
  Purchase #4 $250.55   6.728%   $267.407   $267.41   $267.40   $267.40  
  Purchase #5 $152.79   5.197%   $160.7305   $160.73   $160.75   $160.70  
  Purchase #6 $204.72   3.285%   $211.4451   $211.45   $211.45   $211.40  
  Purchase #7 $62.95   8.713%   $68.4348   $68.43   $68.45   $68.40  
  7 purchase totals = $1,077.56       $1,146.2190   $1,146.23   $1,146.25   $1,146.00