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 $153.59   13.628%   $174.5212   $174.52   $174.50   $174.50  
  Purchase #2 $236.99   12.222%   $265.9549   $265.95   $265.95   $266.00  
  Purchase #3 $182.68   8.240%   $197.7328   $197.73   $197.75   $197.70  
  Purchase #4 $148.60   7.107%   $159.161   $159.16   $159.15   $159.20  
  Purchase #5 $107.70   3.739%   $111.7269   $111.73   $111.75   $111.70  
  Purchase #6 $248.53   3.642%   $257.5815   $257.58   $257.60   $257.60  
  Purchase #7 $174.89   8.532%   $189.8116   $189.81   $189.80   $189.80  
  7 purchase totals = $1,252.98       $1,356.4899   $1,356.48   $1,356.50   $1,356.50