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 $83.71   10.304%   $92.3355   $92.34   $92.35   $92.30  
  Purchase #2 $166.74   3.861%   $173.1778   $173.18   $173.20   $173.20  
  Purchase #3 $208.47   5.542%   $220.0234   $220.02   $220.00   $220.00  
  Purchase #4 $75.57   10.473%   $83.4844   $83.48   $83.50   $83.50  
  Purchase #5 $120.31   6.264%   $127.8462   $127.85   $127.85   $127.80  
  Purchase #6 $157.34   12.519%   $177.0374   $177.04   $177.05   $177.00  
  Purchase #7 $147.87   3.290%   $152.7349   $152.73   $152.75   $152.70  
  7 purchase totals = $960.01       $1,026.6396   $1,026.64   $1,026.70   $1,026.50