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 $206.94   8.860%   $225.2749   $225.27   $225.25   $225.30  
  Purchase #2 $199.31   6.360%   $211.9861   $211.99   $212.00   $212.00  
  Purchase #3 $147.35   5.357%   $155.2435   $155.24   $155.25   $155.20  
  Purchase #4 $82.32   11.301%   $91.623   $91.62   $91.60   $91.60  
  Purchase #5 $131.57   6.194%   $139.7194   $139.72   $139.70   $139.70  
  Purchase #6 $110.45   4.484%   $115.4026   $115.40   $115.40   $115.40  
  Purchase #7 $80.73   8.130%   $87.2933   $87.29   $87.30   $87.30  
  7 purchase totals = $958.67       $1,026.5428   $1,026.53   $1,026.50   $1,026.50