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 $229.65   13.642%   $260.9789   $260.98   $261.00   $261.00  
  Purchase #2 $165.29   3.338%   $170.8074   $170.81   $170.80   $170.80  
  Purchase #3 $106.71   6.368%   $113.5053   $113.51   $113.50   $113.50  
  Purchase #4 $114.45   3.573%   $118.5393   $118.54   $118.55   $118.50  
  Purchase #5 $160.67   8.816%   $174.8347   $174.83   $174.85   $174.80  
  Purchase #6 $102.89   5.693%   $108.7475   $108.75   $108.75   $108.70  
  Purchase #7 $64.89   3.651%   $67.2591   $67.26   $67.25   $67.30  
  7 purchase totals = $944.55       $1,014.6722   $1,014.68   $1,014.70   $1,014.60