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 $46.85   9.321%   $51.2169   $51.22   $51.20   $51.20  
  Purchase #2 $90.27   3.590%   $93.5107   $93.51   $93.50   $93.50  
  Purchase #3 $106.36   9.239%   $116.1866   $116.19   $116.20   $116.20  
  Purchase #4 $228.57   7.515%   $245.747   $245.75   $245.75   $245.70  
  Purchase #5 $39.54   9.469%   $43.284   $43.28   $43.30   $43.30  
  Purchase #6 $234.74   5.244%   $247.0498   $247.05   $247.05   $247.00  
  Purchase #7 $137.27   13.777%   $156.1817   $156.18   $156.20   $156.20  
  7 purchase totals = $883.60       $953.1767   $953.18   $953.20   $953.10