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 $74.52   11.317%   $82.9534   $82.95   $82.95   $83.00  
  Purchase #2 $174.96   10.585%   $193.4795   $193.48   $193.50   $193.50  
  Purchase #3 $12.26   3.323%   $12.6674   $12.67   $12.65   $12.70  
  Purchase #4 $142.75   10.505%   $157.7459   $157.75   $157.75   $157.70  
  Purchase #5 $96.86   5.810%   $102.4876   $102.49   $102.50   $102.50  
  Purchase #6 $116.25   9.413%   $127.1926   $127.19   $127.20   $127.20  
  Purchase #7 $179.32   10.388%   $197.9478   $197.95   $197.95   $197.90  
  7 purchase totals = $796.92       $874.4742   $874.48   $874.50   $874.50