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 $58.65   4.359%   $61.2066   $61.21   $61.20   $61.20  
  Purchase #2 $120.95   6.343%   $128.6219   $128.62   $128.60   $128.60  
  Purchase #3 $16.66   12.519%   $18.7457   $18.75   $18.75   $18.70  
  Purchase #4 $225.38   3.803%   $233.9512   $233.95   $233.95   $234.00  
  Purchase #5 $171.69   11.586%   $191.582   $191.58   $191.60   $191.60  
  Purchase #6 $159.28   4.128%   $165.8551   $165.86   $165.85   $165.90  
  Purchase #7 $95.92   13.629%   $108.9929   $108.99   $109.00   $109.00  
  7 purchase totals = $848.53       $908.9554   $908.96   $908.95   $909.00