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 $202.83   11.642%   $226.4435   $226.44   $226.45   $226.40  
  Purchase #2 $220.98   12.483%   $248.5649   $248.56   $248.55   $248.60  
  Purchase #3 $67.44   12.462%   $75.8444   $75.84   $75.85   $75.80  
  Purchase #4 $176.59   9.401%   $193.1912   $193.19   $193.20   $193.20  
  Purchase #5 $86.99   11.843%   $97.2922   $97.29   $97.30   $97.30  
  Purchase #6 $239.37   10.541%   $264.602   $264.60   $264.60   $264.60  
  Purchase #7 $142.68   12.412%   $160.3894   $160.39   $160.40   $160.40  
  7 purchase totals = $1,136.88       $1,266.3276   $1,266.31   $1,266.35   $1,266.30