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 $142.43   9.225%   $155.5692   $155.57   $155.55   $155.60  
  Purchase #2 $156.80   5.204%   $164.9599   $164.96   $164.95   $165.00  
  Purchase #3 $22.78   3.839%   $23.6545   $23.65   $23.65   $23.70  
  Purchase #4 $234.34   6.108%   $248.6535   $248.65   $248.65   $248.70  
  Purchase #5 $192.71   5.680%   $203.6559   $203.66   $203.65   $203.70  
  Purchase #6 $58.29   12.341%   $65.4836   $65.48   $65.50   $65.50  
  Purchase #7 $149.67   9.242%   $163.5025   $163.50   $163.50   $163.50  
  7 purchase totals = $957.02       $1,025.4791   $1,025.47   $1,025.45   $1,025.70