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 $92.36   12.416%   $103.8274   $103.83   $103.85   $103.80  
  Purchase #2 $76.74   12.552%   $86.3724   $86.37   $86.35   $86.40  
  Purchase #3 $156.49   12.731%   $176.4127   $176.41   $176.40   $176.40  
  Purchase #4 $59.36   9.345%   $64.9072   $64.91   $64.90   $64.90  
  Purchase #5 $151.40   11.154%   $168.2872   $168.29   $168.30   $168.30  
  Purchase #6 $120.52   4.626%   $126.0953   $126.10   $126.10   $126.10  
  Purchase #7 $204.89   6.617%   $218.4476   $218.45   $218.45   $218.40  
  7 purchase totals = $861.76       $944.3498   $944.36   $944.35   $944.30