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 $120.66   5.272%   $127.0212   $127.02   $127.00   $127.00  
  Purchase #2 $237.83   3.532%   $246.2302   $246.23   $246.25   $246.20  
  Purchase #3 $85.39   11.589%   $95.2858   $95.29   $95.30   $95.30  
  Purchase #4 $172.42   7.839%   $185.936   $185.94   $185.95   $185.90  
  Purchase #5 $123.79   6.809%   $132.2189   $132.22   $132.20   $132.20  
  Purchase #6 $90.98   7.827%   $98.101   $98.10   $98.10   $98.10  
  Purchase #7 $65.49   6.200%   $69.5504   $69.55   $69.55   $69.60  
  7 purchase totals = $896.56       $954.3435   $954.35   $954.35   $954.30