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 $56.35   10.102%   $62.0425   $62.04   $62.05   $62.00  
  Purchase #2 $154.51   8.210%   $167.1953   $167.20   $167.20   $167.20  
  Purchase #3 $24.50   11.270%   $27.2612   $27.26   $27.25   $27.30  
  Purchase #4 $174.77   8.127%   $188.9736   $188.97   $188.95   $189.00  
  Purchase #5 $181.59   5.497%   $191.572   $191.57   $191.55   $191.60  
  Purchase #6 $8.72   9.695%   $9.5654   $9.57   $9.55   $9.60  
  Purchase #7 $206.59   8.272%   $223.6791   $223.68   $223.70   $223.70  
  7 purchase totals = $807.03       $870.2891   $870.29   $870.25   $870.40