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 $54.54   11.578%   $60.8546   $60.85   $60.85   $60.90  
  Purchase #2 $217.39   5.568%   $229.4943   $229.49   $229.50   $229.50  
  Purchase #3 $39.79   7.511%   $42.7786   $42.78   $42.80   $42.80  
  Purchase #4 $54.76   5.396%   $57.7148   $57.71   $57.70   $57.70  
  Purchase #5 $9.42   12.194%   $10.5687   $10.57   $10.55   $10.60  
  Purchase #6 $220.28   6.701%   $235.041   $235.04   $235.05   $235.00  
  Purchase #7 $218.82   5.325%   $230.4722   $230.47   $230.45   $230.50  
  7 purchase totals = $815.00       $866.9242   $866.91   $866.90   $867.00