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 $91.56   5.859%   $96.9245   $96.92   $96.90   $96.90  
  Purchase #2 $222.79   3.236%   $229.9995   $230.00   $230.00   $230.00  
  Purchase #3 $126.41   4.407%   $131.9809   $131.98   $132.00   $132.00  
  Purchase #4 $140.68   4.764%   $147.382   $147.38   $147.40   $147.40  
  Purchase #5 $127.61   9.197%   $139.3463   $139.35   $139.35   $139.30  
  Purchase #6 $108.97   3.729%   $113.0335   $113.03   $113.05   $113.00  
  Purchase #7 $66.65   3.819%   $69.1954   $69.20   $69.20   $69.20  
  7 purchase totals = $884.67       $927.8621   $927.86   $927.90   $927.80