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 $222.64   8.651%   $241.9006   $241.90   $241.90   $241.90  
  Purchase #2 $219.88   7.115%   $235.5245   $235.52   $235.50   $235.50  
  Purchase #3 $64.92   6.762%   $69.3099   $69.31   $69.30   $69.30  
  Purchase #4 $168.61   12.126%   $189.0556   $189.06   $189.05   $189.10  
  Purchase #5 $59.61   11.461%   $66.4419   $66.44   $66.45   $66.40  
  Purchase #6 $38.63   11.827%   $43.1988   $43.20   $43.20   $43.20  
  Purchase #7 $207.83   5.700%   $219.6763   $219.68   $219.70   $219.70  
  7 purchase totals = $982.12       $1,065.1076   $1,065.11   $1,065.10   $1,065.10