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 $137.95   10.316%   $152.1809   $152.18   $152.20   $152.20  
  Purchase #2 $241.94   10.781%   $268.0236   $268.02   $268.00   $268.00  
  Purchase #3 $134.47   13.521%   $152.6517   $152.65   $152.65   $152.70  
  Purchase #4 $22.49   3.115%   $23.1906   $23.19   $23.20   $23.20  
  Purchase #5 $194.75   3.760%   $202.0726   $202.07   $202.05   $202.10  
  Purchase #6 $243.94   10.655%   $269.9318   $269.93   $269.95   $269.90  
  Purchase #7 $24.30   12.786%   $27.407   $27.41   $27.40   $27.40  
  7 purchase totals = $999.84       $1,095.4582   $1,095.45   $1,095.45   $1,095.50