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 $212.32   9.258%   $231.9766   $231.98   $232.00   $232.00  
  Purchase #2 $32.64   4.833%   $34.2175   $34.22   $34.20   $34.20  
  Purchase #3 $140.35   7.788%   $151.2805   $151.28   $151.30   $151.30  
  Purchase #4 $210.94   6.482%   $224.6131   $224.61   $224.60   $224.60  
  Purchase #5 $58.88   6.162%   $62.5082   $62.51   $62.50   $62.50  
  Purchase #6 $243.97   9.621%   $267.4424   $267.44   $267.45   $267.40  
  Purchase #7 $51.66   12.161%   $57.9424   $57.94   $57.95   $57.90  
  7 purchase totals = $950.76       $1,029.9807   $1,029.98   $1,030.00   $1,029.90