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 $185.33   11.753%   $207.1118   $207.11   $207.10   $207.10  
  Purchase #2 $85.39   12.310%   $95.9015   $95.90   $95.90   $95.90  
  Purchase #3 $147.47   4.155%   $153.5974   $153.60   $153.60   $153.60  
  Purchase #4 $47.60   6.514%   $50.7007   $50.70   $50.70   $50.70  
  Purchase #5 $93.93   5.647%   $99.2342   $99.23   $99.25   $99.20  
  Purchase #6 $140.51   3.560%   $145.5122   $145.51   $145.50   $145.50  
  Purchase #7 $229.91   5.349%   $242.2079   $242.21   $242.20   $242.20  
  7 purchase totals = $930.14       $994.2657   $994.26   $994.25   $994.20