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 $188.97   6.505%   $201.2625   $201.26   $201.25   $201.30  
  Purchase #2 $215.25   10.838%   $238.5788   $238.58   $238.60   $238.60  
  Purchase #3 $247.29   3.551%   $256.0713   $256.07   $256.05   $256.10  
  Purchase #4 $167.37   11.822%   $187.1565   $187.16   $187.15   $187.20  
  Purchase #5 $134.95   13.777%   $153.5421   $153.54   $153.55   $153.50  
  Purchase #6 $138.43   5.325%   $145.8014   $145.80   $145.80   $145.80  
  Purchase #7 $60.41   5.277%   $63.5978   $63.60   $63.60   $63.60  
  7 purchase totals = $1,152.67       $1,246.0104   $1,246.01   $1,246.00   $1,246.10