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 $232.76   10.724%   $257.7212   $257.72   $257.70   $257.70  
  Purchase #2 $119.81   8.656%   $130.1808   $130.18   $130.20   $130.20  
  Purchase #3 $248.94   9.421%   $272.3926   $272.39   $272.40   $272.40  
  Purchase #4 $233.47   8.346%   $252.9554   $252.96   $252.95   $253.00  
  Purchase #5 $219.35   5.107%   $230.5522   $230.55   $230.55   $230.60  
  Purchase #6 $86.98   6.370%   $92.5206   $92.52   $92.50   $92.50  
  Purchase #7 $248.70   7.513%   $267.3848   $267.38   $267.40   $267.40  
  7 purchase totals = $1,390.01       $1,503.7076   $1,503.70   $1,503.70   $1,503.80