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 $67.68   8.259%   $73.2697   $73.27   $73.25   $73.30  
  Purchase #2 $192.85   5.318%   $203.1058   $203.11   $203.10   $203.10  
  Purchase #3 $78.85   11.545%   $87.9532   $87.95   $87.95   $88.00  
  Purchase #4 $115.86   6.868%   $123.8173   $123.82   $123.80   $123.80  
  Purchase #5 $150.35   11.870%   $168.1965   $168.20   $168.20   $168.20  
  Purchase #6 $215.32   3.587%   $223.0435   $223.04   $223.05   $223.00  
  Purchase #7 $141.99   3.744%   $147.3061   $147.31   $147.30   $147.30  
  7 purchase totals = $962.90       $1,026.6921   $1,026.70   $1,026.65   $1,026.70