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 $238.65   9.820%   $262.0854   $262.09   $262.10   $262.10  
  Purchase #2 $120.49   4.423%   $125.8193   $125.82   $125.80   $125.80  
  Purchase #3 $123.88   11.514%   $138.1435   $138.14   $138.15   $138.10  
  Purchase #4 $248.89   5.399%   $262.3276   $262.33   $262.35   $262.30  
  Purchase #5 $132.61   6.134%   $140.7443   $140.74   $140.75   $140.70  
  Purchase #6 $45.28   9.656%   $49.6522   $49.65   $49.65   $49.70  
  Purchase #7 $51.33   11.755%   $57.3638   $57.36   $57.35   $57.40  
  7 purchase totals = $961.13       $1,036.1361   $1,036.13   $1,036.15   $1,036.10