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 $211.62   11.771%   $236.5298   $236.53   $236.55   $236.50  
  Purchase #2 $244.92   12.836%   $276.3579   $276.36   $276.35   $276.40  
  Purchase #3 $247.97   11.121%   $275.5467   $275.55   $275.55   $275.50  
  Purchase #4 $198.60   10.689%   $219.8284   $219.83   $219.85   $219.80  
  Purchase #5 $110.26   8.399%   $119.5207   $119.52   $119.50   $119.50  
  Purchase #6 $161.48   8.222%   $174.7569   $174.76   $174.75   $174.80  
  Purchase #7 $39.41   6.253%   $41.8743   $41.87   $41.85   $41.90  
  7 purchase totals = $1,214.26       $1,344.4147   $1,344.42   $1,344.40   $1,344.40