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 $31.45   10.122%   $34.6334   $34.63   $34.65   $34.60  
  Purchase #2 $189.75   9.524%   $207.8218   $207.82   $207.80   $207.80  
  Purchase #3 $183.70   9.795%   $201.6934   $201.69   $201.70   $201.70  
  Purchase #4 $203.79   10.424%   $225.0331   $225.03   $225.05   $225.00  
  Purchase #5 $171.78   8.564%   $186.4912   $186.49   $186.50   $186.50  
  Purchase #6 $144.79   4.780%   $151.711   $151.71   $151.70   $151.70  
  Purchase #7 $36.26   10.193%   $39.956   $39.96   $39.95   $40.00  
  7 purchase totals = $961.52       $1,047.3399   $1,047.33   $1,047.35   $1,047.30