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 $52.30   10.413%   $57.746   $57.75   $57.75   $57.70  
  Purchase #2 $33.39   6.708%   $35.6298   $35.63   $35.65   $35.60  
  Purchase #3 $232.51   12.145%   $260.7483   $260.75   $260.75   $260.70  
  Purchase #4 $14.48   9.574%   $15.8663   $15.87   $15.85   $15.90  
  Purchase #5 $169.49   6.798%   $181.0119   $181.01   $181.00   $181.00  
  Purchase #6 $106.92   6.546%   $113.919   $113.92   $113.90   $113.90  
  Purchase #7 $221.40   4.305%   $230.9313   $230.93   $230.95   $230.90  
  7 purchase totals = $830.49       $895.8526   $895.86   $895.85   $895.70