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 $153.45   7.717%   $165.2917   $165.29   $165.30   $165.30  
  Purchase #2 $11.30   6.299%   $12.0118   $12.01   $12.00   $12.00  
  Purchase #3 $169.25   3.120%   $174.5306   $174.53   $174.55   $174.50  
  Purchase #4 $220.95   7.279%   $237.033   $237.03   $237.05   $237.00  
  Purchase #5 $225.57   3.163%   $232.7048   $232.70   $232.70   $232.70  
  Purchase #6 $233.86   4.730%   $244.9216   $244.92   $244.90   $244.90  
  Purchase #7 $47.69   6.135%   $50.6158   $50.62   $50.60   $50.60  
  7 purchase totals = $1,062.07       $1,117.1093   $1,117.10   $1,117.10   $1,117.00