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 $90.72   5.625%   $95.823   $95.82   $95.80   $95.80  
  Purchase #2 $55.48   5.823%   $58.7106   $58.71   $58.70   $58.70  
  Purchase #3 $32.83   3.539%   $33.9919   $33.99   $34.00   $34.00  
  Purchase #4 $24.28   8.270%   $26.288   $26.29   $26.30   $26.30  
  Purchase #5 $166.83   5.331%   $175.7237   $175.72   $175.70   $175.70  
  Purchase #6 $170.50   13.172%   $192.9583   $192.96   $192.95   $193.00  
  Purchase #7 $163.93   10.223%   $180.6886   $180.69   $180.70   $180.70  
  7 purchase totals = $704.57       $764.1841   $764.18   $764.15   $764.20