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 $54.93   11.442%   $61.2151   $61.22   $61.20   $61.20  
  Purchase #2 $146.35   12.790%   $165.0682   $165.07   $165.05   $165.10  
  Purchase #3 $145.31   6.472%   $154.7145   $154.71   $154.70   $154.70  
  Purchase #4 $67.39   3.618%   $69.8282   $69.83   $69.85   $69.80  
  Purchase #5 $11.57   6.662%   $12.3408   $12.34   $12.35   $12.30  
  Purchase #6 $189.62   4.566%   $198.278   $198.28   $198.30   $198.30  
  Purchase #7 $98.45   12.360%   $110.6184   $110.62   $110.60   $110.60  
  7 purchase totals = $713.62       $772.0632   $772.07   $772.05   $772.00