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 $84.46   9.552%   $92.5276   $92.53   $92.55   $92.50  
  Purchase #2 $29.48   7.190%   $31.5996   $31.60   $31.60   $31.60  
  Purchase #3 $218.88   4.379%   $228.4648   $228.46   $228.45   $228.50  
  Purchase #4 $36.25   10.736%   $40.1418   $40.14   $40.15   $40.10  
  Purchase #5 $152.84   5.837%   $161.7613   $161.76   $161.75   $161.80  
  Purchase #6 $15.30   5.226%   $16.0996   $16.10   $16.10   $16.10  
  Purchase #7 $160.79   12.814%   $181.3936   $181.39   $181.40   $181.40  
  7 purchase totals = $698.00       $751.9883   $751.98   $752.00   $752.00