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 $92.78   3.148%   $95.7007   $95.70   $95.70   $95.70  
  Purchase #2 $86.87   9.756%   $95.345   $95.35   $95.35   $95.30  
  Purchase #3 $244.93   13.338%   $277.5988   $277.60   $277.60   $277.60  
  Purchase #4 $78.90   12.711%   $88.929   $88.93   $88.95   $88.90  
  Purchase #5 $163.30   11.264%   $181.6941   $181.69   $181.70   $181.70  
  Purchase #6 $43.32   8.194%   $46.8696   $46.87   $46.85   $46.90  
  Purchase #7 $116.73   8.628%   $126.8015   $126.80   $126.80   $126.80  
  7 purchase totals = $826.83       $912.9387   $912.94   $912.95   $912.90