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 $110.67   13.817%   $125.9613   $125.96   $125.95   $126.00  
  Purchase #2 $250.99   7.712%   $270.3463   $270.35   $270.35   $270.30  
  Purchase #3 $29.92   12.159%   $33.558   $33.56   $33.55   $33.60  
  Purchase #4 $220.65   12.779%   $248.8469   $248.85   $248.85   $248.80  
  Purchase #5 $73.53   8.588%   $79.8448   $79.84   $79.85   $79.80  
  Purchase #6 $121.83   7.540%   $131.016   $131.02   $131.00   $131.00  
  Purchase #7 $180.91   7.814%   $195.0463   $195.05   $195.05   $195.00  
  7 purchase totals = $988.50       $1,084.6196   $1,084.63   $1,084.60   $1,084.50