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 $56.27   3.718%   $58.3621   $58.36   $58.35   $58.40  
  Purchase #2 $32.83   11.157%   $36.4928   $36.49   $36.50   $36.50  
  Purchase #3 $197.71   3.283%   $204.2008   $204.20   $204.20   $204.20  
  Purchase #4 $239.92   6.270%   $254.963   $254.96   $254.95   $255.00  
  Purchase #5 $110.76   9.745%   $121.5536   $121.55   $121.55   $121.60  
  Purchase #6 $204.96   8.726%   $222.8448   $222.84   $222.85   $222.80  
  Purchase #7 $174.61   6.687%   $186.2862   $186.29   $186.30   $186.30  
  7 purchase totals = $1,017.06       $1,084.7033   $1,084.69   $1,084.70   $1,084.80