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 $34.58   6.751%   $36.9145   $36.91   $36.90   $36.90  
  Purchase #2 $181.93   8.623%   $197.6178   $197.62   $197.60   $197.60  
  Purchase #3 $87.44   10.592%   $96.7016   $96.70   $96.70   $96.70  
  Purchase #4 $59.62   9.437%   $65.2463   $65.25   $65.25   $65.20  
  Purchase #5 $113.39   10.127%   $124.873   $124.87   $124.85   $124.90  
  Purchase #6 $11.30   5.272%   $11.8957   $11.90   $11.90   $11.90  
  Purchase #7 $49.65   11.373%   $55.2967   $55.30   $55.30   $55.30  
  7 purchase totals = $537.91       $588.5456   $588.55   $588.50   $588.50