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 $64.78   5.267%   $68.192   $68.19   $68.20   $68.20  
  Purchase #2 $248.46   5.469%   $262.0483   $262.05   $262.05   $262.00  
  Purchase #3 $115.93   9.366%   $126.788   $126.79   $126.80   $126.80  
  Purchase #4 $49.75   7.152%   $53.3081   $53.31   $53.30   $53.30  
  Purchase #5 $225.75   13.420%   $256.0457   $256.05   $256.05   $256.00  
  Purchase #6 $110.31   4.703%   $115.4979   $115.50   $115.50   $115.50  
  Purchase #7 $131.35   12.364%   $147.5901   $147.59   $147.60   $147.60  
  7 purchase totals = $946.33       $1,029.4701   $1,029.48   $1,029.50   $1,029.40