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 $158.85   12.762%   $179.1224   $179.12   $179.10   $179.10  
  Purchase #2 $204.77   8.820%   $222.8307   $222.83   $222.85   $222.80  
  Purchase #3 $61.85   8.307%   $66.9879   $66.99   $67.00   $67.00  
  Purchase #4 $178.69   4.296%   $186.3665   $186.37   $186.35   $186.40  
  Purchase #5 $141.59   10.133%   $155.9373   $155.94   $155.95   $155.90  
  Purchase #6 $164.92   5.809%   $174.5002   $174.50   $174.50   $174.50  
  Purchase #7 $40.26   11.679%   $44.962   $44.96   $44.95   $45.00  
  7 purchase totals = $950.93       $1,030.7070   $1,030.71   $1,030.70   $1,030.70