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 $96.29   11.341%   $107.2102   $107.21   $107.20   $107.20  
  Purchase #2 $117.27   7.106%   $125.6032   $125.60   $125.60   $125.60  
  Purchase #3 $84.96   5.191%   $89.3703   $89.37   $89.35   $89.40  
  Purchase #4 $164.67   3.791%   $170.9126   $170.91   $170.90   $170.90  
  Purchase #5 $103.64   8.709%   $112.666   $112.67   $112.65   $112.70  
  Purchase #6 $225.85   11.271%   $251.3056   $251.31   $251.30   $251.30  
  Purchase #7 $137.47   11.781%   $153.6653   $153.67   $153.65   $153.70  
  7 purchase totals = $930.15       $1,010.7332   $1,010.74   $1,010.65   $1,010.80