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 $79.41   10.814%   $87.9974   $88.00   $88.00   $88.00  
  Purchase #2 $235.29   9.356%   $257.3037   $257.30   $257.30   $257.30  
  Purchase #3 $143.83   8.736%   $156.395   $156.40   $156.40   $156.40  
  Purchase #4 $157.76   3.832%   $163.8054   $163.81   $163.80   $163.80  
  Purchase #5 $161.54   13.561%   $183.4464   $183.45   $183.45   $183.40  
  Purchase #6 $37.65   8.496%   $40.8487   $40.85   $40.85   $40.80  
  Purchase #7 $149.30   6.822%   $159.4852   $159.49   $159.50   $159.50  
  7 purchase totals = $964.78       $1,049.2818   $1,049.30   $1,049.30   $1,049.20