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 $204.33   10.627%   $226.0441   $226.04   $226.05   $226.00  
  Purchase #2 $165.83   3.247%   $171.2145   $171.21   $171.20   $171.20  
  Purchase #3 $29.43   8.707%   $31.9925   $31.99   $32.00   $32.00  
  Purchase #4 $45.91   12.334%   $51.5725   $51.57   $51.55   $51.60  
  Purchase #5 $48.74   11.801%   $54.4918   $54.49   $54.50   $54.50  
  Purchase #6 $99.28   11.492%   $110.6893   $110.69   $110.70   $110.70  
  Purchase #7 $57.43   5.801%   $60.7615   $60.76   $60.75   $60.80  
  7 purchase totals = $650.95       $706.7662   $706.75   $706.75   $706.80