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 $79.52   11.250%   $88.466   $88.47   $88.45   $88.50  
  Purchase #2 $224.81   12.784%   $253.5497   $253.55   $253.55   $253.50  
  Purchase #3 $32.92   10.351%   $36.3275   $36.33   $36.35   $36.30  
  Purchase #4 $72.25   6.584%   $77.0069   $77.01   $77.00   $77.00  
  Purchase #5 $197.52   4.654%   $206.7126   $206.71   $206.70   $206.70  
  Purchase #6 $86.52   9.851%   $95.0431   $95.04   $95.05   $95.00  
  Purchase #7 $137.43   7.134%   $147.2343   $147.23   $147.25   $147.20  
  7 purchase totals = $830.97       $904.3401   $904.34   $904.35   $904.20