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 $228.83   8.578%   $248.459   $248.46   $248.45   $248.50  
  Purchase #2 $35.47   5.536%   $37.4336   $37.43   $37.45   $37.40  
  Purchase #3 $45.65   9.579%   $50.0228   $50.02   $50.00   $50.00  
  Purchase #4 $168.35   3.499%   $174.2406   $174.24   $174.25   $174.20  
  Purchase #5 $180.74   12.510%   $203.3506   $203.35   $203.35   $203.40  
  Purchase #6 $212.46   7.325%   $228.0227   $228.02   $228.00   $228.00  
  Purchase #7 $182.54   5.682%   $192.9119   $192.91   $192.90   $192.90  
  7 purchase totals = $1,054.04       $1,134.4412   $1,134.43   $1,134.40   $1,134.40