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 $85.29   11.476%   $95.0779   $95.08   $95.10   $95.10  
  Purchase #2 $177.96   8.350%   $192.8197   $192.82   $192.80   $192.80  
  Purchase #3 $45.34   7.802%   $48.8774   $48.88   $48.90   $48.90  
  Purchase #4 $185.28   7.503%   $199.1816   $199.18   $199.20   $199.20  
  Purchase #5 $86.99   5.206%   $91.5187   $91.52   $91.50   $91.50  
  Purchase #6 $198.29   3.865%   $205.9539   $205.95   $205.95   $206.00  
  Purchase #7 $33.34   6.288%   $35.4364   $35.44   $35.45   $35.40  
  7 purchase totals = $812.49       $868.8656   $868.87   $868.90   $868.90