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 $206.59   11.661%   $230.6805   $230.68   $230.70   $230.70  
  Purchase #2 $63.43   3.818%   $65.8518   $65.85   $65.85   $65.90  
  Purchase #3 $123.32   3.649%   $127.8199   $127.82   $127.80   $127.80  
  Purchase #4 $211.98   9.499%   $232.116   $232.12   $232.10   $232.10  
  Purchase #5 $75.38   8.367%   $81.687   $81.69   $81.70   $81.70  
  Purchase #6 $218.49   6.640%   $232.9977   $233.00   $233.00   $233.00  
  Purchase #7 $28.95   12.610%   $32.6006   $32.60   $32.60   $32.60  
  7 purchase totals = $928.14       $1,003.7535   $1,003.76   $1,003.75   $1,003.80