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 $22.57   10.561%   $24.9536   $24.95   $24.95   $25.00  
  Purchase #2 $55.45   9.463%   $60.6972   $60.70   $60.70   $60.70  
  Purchase #3 $150.56   3.118%   $155.2545   $155.25   $155.25   $155.30  
  Purchase #4 $165.36   8.854%   $180.001   $180.00   $180.00   $180.00  
  Purchase #5 $50.61   10.735%   $56.043   $56.04   $56.05   $56.00  
  Purchase #6 $181.74   9.783%   $199.5196   $199.52   $199.50   $199.50  
  Purchase #7 $63.82   10.232%   $70.3501   $70.35   $70.35   $70.40  
  7 purchase totals = $690.11       $746.8190   $746.81   $746.80   $746.90