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 $98.84   9.480%   $108.21   $108.21   $108.20   $108.20  
  Purchase #2 $88.58   5.387%   $93.3518   $93.35   $93.35   $93.40  
  Purchase #3 $115.59   13.564%   $131.2686   $131.27   $131.25   $131.30  
  Purchase #4 $135.28   7.754%   $145.7696   $145.77   $145.75   $145.80  
  Purchase #5 $66.66   10.572%   $73.7073   $73.71   $73.70   $73.70  
  Purchase #6 $132.52   6.430%   $141.041   $141.04   $141.05   $141.00  
  Purchase #7 $63.60   5.341%   $66.9969   $67.00   $67.00   $67.00  
  7 purchase totals = $701.07       $760.3452   $760.35   $760.30   $760.40