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 $214.28   8.270%   $232.001   $232.00   $232.00   $232.00  
  Purchase #2 $165.27   11.693%   $184.595   $184.60   $184.60   $184.60  
  Purchase #3 $9.81   10.313%   $10.8217   $10.82   $10.80   $10.80  
  Purchase #4 $31.76   3.642%   $32.9167   $32.92   $32.90   $32.90  
  Purchase #5 $160.75   9.792%   $176.4906   $176.49   $176.50   $176.50  
  Purchase #6 $237.43   13.408%   $269.2646   $269.26   $269.25   $269.30  
  Purchase #7 $102.72   8.834%   $111.7943   $111.79   $111.80   $111.80  
  7 purchase totals = $922.02       $1,017.8839   $1,017.88   $1,017.85   $1,017.90