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 $208.86   8.414%   $226.4335   $226.43   $226.45   $226.40  
  Purchase #2 $74.46   12.394%   $83.6886   $83.69   $83.70   $83.70  
  Purchase #3 $244.91   4.323%   $255.4975   $255.50   $255.50   $255.50  
  Purchase #4 $14.92   9.558%   $16.3461   $16.35   $16.35   $16.30  
  Purchase #5 $237.86   3.487%   $246.1542   $246.15   $246.15   $246.20  
  Purchase #6 $43.62   13.603%   $49.5536   $49.55   $49.55   $49.60  
  Purchase #7 $150.45   4.764%   $157.6174   $157.62   $157.60   $157.60  
  7 purchase totals = $975.08       $1,035.2909   $1,035.29   $1,035.30   $1,035.30