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 $93.52   13.304%   $105.9619   $105.96   $105.95   $106.00  
  Purchase #2 $151.76   5.821%   $160.5939   $160.59   $160.60   $160.60  
  Purchase #3 $154.95   12.408%   $174.1762   $174.18   $174.20   $174.20  
  Purchase #4 $115.95   7.279%   $124.39   $124.39   $124.40   $124.40  
  Purchase #5 $163.46   7.475%   $175.6786   $175.68   $175.70   $175.70  
  Purchase #6 $226.33   6.668%   $241.4217   $241.42   $241.40   $241.40  
  Purchase #7 $89.53   8.357%   $97.012   $97.01   $97.00   $97.00  
  7 purchase totals = $995.50       $1,079.2343   $1,079.23   $1,079.25   $1,079.30