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 $148.53   11.730%   $165.9526   $165.95   $165.95   $166.00  
  Purchase #2 $120.80   12.569%   $135.9834   $135.98   $136.00   $136.00  
  Purchase #3 $146.39   9.651%   $160.5181   $160.52   $160.50   $160.50  
  Purchase #4 $61.25   3.563%   $63.4323   $63.43   $63.45   $63.40  
  Purchase #5 $60.86   6.510%   $64.822   $64.82   $64.80   $64.80  
  Purchase #6 $151.94   8.597%   $165.0023   $165.00   $165.00   $165.00  
  Purchase #7 $14.28   11.282%   $15.8911   $15.89   $15.90   $15.90  
  7 purchase totals = $704.05       $771.6018   $771.59   $771.60   $771.60