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 $223.49   10.162%   $246.2011   $246.20   $246.20   $246.20  
  Purchase #2 $150.38   4.405%   $157.0042   $157.00   $157.00   $157.00  
  Purchase #3 $209.29   6.325%   $222.5276   $222.53   $222.55   $222.50  
  Purchase #4 $138.26   10.253%   $152.4358   $152.44   $152.45   $152.40  
  Purchase #5 $74.96   12.804%   $84.5579   $84.56   $84.55   $84.60  
  Purchase #6 $193.45   10.696%   $214.1414   $214.14   $214.15   $214.10  
  Purchase #7 $76.84   7.755%   $82.7989   $82.80   $82.80   $82.80  
  7 purchase totals = $1,066.67       $1,159.6669   $1,159.67   $1,159.70   $1,159.60