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 $156.97   5.482%   $165.5751   $165.58   $165.60   $165.60  
  Purchase #2 $157.30   11.221%   $174.9506   $174.95   $174.95   $175.00  
  Purchase #3 $43.45   6.308%   $46.1908   $46.19   $46.20   $46.20  
  Purchase #4 $181.59   4.260%   $189.3257   $189.33   $189.35   $189.30  
  Purchase #5 $225.66   9.202%   $246.4252   $246.43   $246.45   $246.40  
  Purchase #6 $61.51   12.766%   $69.3624   $69.36   $69.35   $69.40  
  Purchase #7 $124.84   5.749%   $132.0171   $132.02   $132.00   $132.00  
  7 purchase totals = $951.32       $1,023.8469   $1,023.86   $1,023.90   $1,023.90