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 $52.72   5.399%   $55.5664   $55.57   $55.55   $55.60  
  Purchase #2 $222.74   4.126%   $231.9303   $231.93   $231.95   $231.90  
  Purchase #3 $117.29   6.565%   $124.9901   $124.99   $125.00   $125.00  
  Purchase #4 $198.37   12.180%   $222.5315   $222.53   $222.55   $222.50  
  Purchase #5 $188.55   12.786%   $212.658   $212.66   $212.65   $212.70  
  Purchase #6 $247.97   8.530%   $269.1218   $269.12   $269.10   $269.10  
  Purchase #7 $30.82   6.322%   $32.7684   $32.77   $32.75   $32.80  
  7 purchase totals = $1,058.46       $1,149.5665   $1,149.57   $1,149.55   $1,149.60