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 $70.52   8.708%   $76.6609   $76.66   $76.65   $76.70  
  Purchase #2 $233.66   13.855%   $266.0336   $266.03   $266.05   $266.00  
  Purchase #3 $195.72   4.118%   $203.7797   $203.78   $203.80   $203.80  
  Purchase #4 $147.90   6.242%   $157.1319   $157.13   $157.15   $157.10  
  Purchase #5 $84.81   11.233%   $94.3367   $94.34   $94.35   $94.30  
  Purchase #6 $207.56   4.683%   $217.28   $217.28   $217.30   $217.30  
  Purchase #7 $129.78   12.188%   $145.5976   $145.60   $145.60   $145.60  
  7 purchase totals = $1,069.95       $1,160.8204   $1,160.82   $1,160.90   $1,160.80